>>Tonight, two stories from Syria in this special edition of Frontline.

First, as the fighting rages, Frontline is embedded with rebel leaders.

>>This is the front line of Aleppo.

You meet people in the morning, and at the end of the day, they're dead.

>>With them, street to street, as they fight Assad's army.

>>We are returning now, after the attack.

It just shows you how brave they are, and at the same time, how disorganized they are.

>>Guardian correspondent for Frontline, Ghaith Abdul-Ahad, takes you inside the battle for Syria.

And later tonight, the regime fights back.

>>The regime now is bombarding civilian neighborhoods with artillery, with tank fire, and with fighter bombers.

>>How is President Bashar al-Assad holding on to power?

>>The Iranians are gaining influence in Syria now by the day.

>>And what will happen if Assad falls?

>>There is definitely increasing worry in the United States administration about in whose hands these weapons are falling.

>>These two stories on this special edition ofFrontline.

>>NARRATOR: Guardian reporter Ghaith Abdul-Ahad's journey into Syria began five weeks ago on a supply route the rebels use to bring weapons from neighboring Turkey.

>>This is all liberated territory at the moment.

>>NARRATOR: The rebels are fighting to overthrow President Bashar al-Assad.

Every night the supply route is attacked by his regime's aircraft and helicopters.

>>As we're driving, we see another car is coming our way.

People crossing back into Turkey, refugees.

>>NARRATOR: Ghaith was on his way to meet up with the rebels who were fighting in Syria's biggest city and commercial hub, Aleppo.

>>This is the most important battle in Syria.

Through the battle of Aleppo, we can see the future of the Syrian revolution.

>>NARRATOR: By dawn, Ghaith had reached a rebel staging post just a few miles outside of Aleppo.

Fighters had just arrived fresh from battle.

They call themselves the Free Syrian Army.

Their commander, Abu Bakri, said they now controlled half the city but that government forces were advancing.

>>(translated): The day before yesterday, there was increased artillery shelling and shooting of mortars and MiG planes attacked.

We've retreated to create a second defensive line so we can counterattack.

>>NARRATOR: Abu Bakri never expected to be a rebel commander.

>>(translated): I finished compulsory military service in 2006, and by Allah's grace went on to study economics at the University of Aleppo.

That was me until the revolution started.

>>Takbir.

>>Allahu Akbar.

>>Takbir.

>>Allahu Akbar.

>>NARRATOR: Ghaith continued his journey into Aleppo.

Abu Bakri said God willing he'd see him on the front line in two days.

>>We are being smuggled into Aleppo by rebels and activists.

We're taking a long route through side streets, through residential neighborhoods and through villages, and it's a very complicated process.

We have scouts moving ahead of us.

We crossed a couple of the streets, and then we started hearing the bullets, the shelling, the machine gun fire.

(machine gun fire) (explosion) >>NARRATOR: Ghaith reached one of the first rebel positions in Aleppo.

Government soldiers had advanced to a building close by.

The rebels were preparing to counterattack.

(gunfire) >>We are withdrawing now after the attack.

They fired into the street, and after almost half an hour of shooting, now they're withdrawing.

It just basically shows you how brave they are-- they go into the middle of the street firing at a government position-- yet at the same time how disorganized they are.

Now we're crossing the street.

They're kind of fearing a sniper.

The battle of Aleppo is hanging in the balance.

It's being fought over in every single street, neighborhood, along these front lines.

The whole city become the playground of fighters, of tanks, of soldiers.

>>NARRATOR: Back at their command post, the fighters discovered five of their men were missing.

>>NARRATOR: Then the fighters returned.

With them was a Syrian soldier who'd just switched sides.

>>NARRATOR: He was welcomed as a hero.

(gunfire) (cheering) >>Allahu Akbar!

(gunfire, explosion) >>NARRATOR: Ghaith traveled farther into Aleppo.

>>Destroyed buildings, destroyed apartment houses, festering garbage-- the smell was killing-- bullet casing, debris on the ground.

We're just passing very quickly from a sniper alleyway.

>>NARRATOR: His destination-- a neighborhood that's seen some of the fiercest fighting, Salahuddin.

(gunfire) >>We're really on the edge of Salahuddin.

The Free Syrian Army had been retreating heavily in the past couple of days-- they've been losing men, they've been losing ammunition.

This is the last stand in Salahuddin.

They've just got reinforcement, trying to protect the next neighborhood after Salahuddin.

>>NARRATOR: The man who coordinates the 150 fighters in this key sector is Abu Mohammed.

>>Abu Mohammed is a very, very important character, a member of the Aleppo Military Council.

Through him brand new ammunition, brand new weapons are being channeled into the rebels.

>>NARRATOR: He was asking the fighters to stand firm.

(explosion) >>NARRATOR: Until eight months ago, he was a captain in the Syrian army.

>>Here is a man who believes we're trying to build a democracy, we're trying to build a free Syria.

>>NARRATOR: Abu Mohammed agreed to take Ghaith with him as he delivered ammunition to the rebel units.

The front line was changing by the minute.

>>A street that was under the control of the rebels in the morning can switch sides in the afternoon and the government can take over that street.

>>NARRATOR: They began their journey along the rebel front line in the Salahuddin neighborhood.

>>He's trying to coordinate all these different units, be it Islamist, be it jihadis, be it secular, be it village-based unit.

The only thing that was connecting all these units was the ammunition delivered by Abu Mohammed.

>>They've been doing this all day.

They tour the front lines, they go from one position to the other, and they fill the gaps in terms of men and ammunition and bullets.

>>This is one of the many, many front lines in Aleppo.

There's a sniper down this alley.

There's a position of the Free Syrian Army here and they're trying to get them ammunition.

(explosion) (explosion) It's the scariest sound in a war zone.

It's this roar of this tank coming down the street, so we just run.

Tank's coming.

We were just around the corner when they were trying to sneak into behind the tank, when the tank just came so close to the corner and we had to run to the car and... >>NARRATOR: Abu Mohammed makes this dangerous ammunition run every day.

Today's run was successful.

The fighters had held their line.

>>(translated): Most of our soldiers are civilians.

In the army there is a principle of discipline.

If you order a soldier to do something and he doesn't carry it out, you can discipline him.

But you can't do that here.

We have no discipline.

And this is one of the fundamental problems.

They don't follow directions; we make plans and they don't abide by them.

If they follow 15% of the plans, that is great.

>>NARRATOR: Abu Mohammed took a call from a fighter.

>>NARRATOR: The fighter was pleading for more ammunition.

His unit was being attacked by a tank.

Abu Mohammed sent 300 bullets and two rocket-propelled grenades-- half of all that he had.

Abu Mohammed then told us about the government's strategy.

>>(translated): Its strategy is artillery bombardment, the tanks advance, then plant snipers before pulling the tanks back.

The snipers' role is to clear the area in front, and then next day, the tanks move forward beyond the snipers.

And then the snipers advance again.

>>NARRATOR: Suddenly, outside headquarters, there was a new threat.

>>They say the tank is trying to advance.

The guys just scrambled some force and they came around the corner here and they're trying to stop it.

This is the front line now.

The guys are trying to protect this corner of the street in the battle of Aleppo.

(gunfire) >>NARRATOR: A few streets away, a garden had become a frontline cemetery.

This is where the next casualties would be buried.

(gunfire) Close by, a deadly fight had ended.

Abu Mohammed's fighters had just killed two snipers.

>>NARRATOR: They believed it was now safe to retrieve the bodies of five dead civilians.

A husband's arm was still draped around his wife in a final attempt to protect her.

Their son lay in the back.

>>Did they die immediately?

Did they bleed to death?

Did they hear the shots?

How scared were they?

That image, I don't think it will leave me ever.

>>NARRATOR: A sniper opened fire.

The bodies had to remain unburied.

Moments later, to their surprise, the fighters had to stop this man and his daughters from walking into the line of fire.

They lived nearby.

>>They think themselves immune to the shelling, to the snipers bullets.

They think it only happens to the fighters.

>>NARRATOR: Locals came out to buy bread from a bakery.

In this city of over two million, thousands of people continue to live in what is a battlefield rather than flee to refugee camps in neighboring Turkey.

One man, who didn't want to reveal his identity, told us why he was risking his life.

>>NARRATOR: Ghaith saw government aircraft, helicopters, and artillery shelling and bombing indiscriminately.

>>We saw a small plane flying very low, and it curved low into the area and dropped one bomb, in the corner of a house, far away from where the rebels are.

It basically shows you how, you know, how they're missing the rebels but they are actually hitting the civilian targets.

>>NARRATOR: A local resident berated the rebel fighter for bringing the battle to his city.

>>NARRATOR: That night, an artillery shell destroyed a nearby house.

>>I think the bombing is so nerve wracking, you get used to the kaboom, the whoosh and the explosion, There's different kinds of explosions.

We get used to them.

But then they fall on a house, then they fall on an apartment building, then they kill civilians.

So it's not only a sound on the background, it has a real impact on the population.

>>NARRATOR: The house owner was killed.

Days before, he'd sent his family to safety.

The next day, reinforcements arrived to help defend the Salahuddin neighborhood.

They were led by Abu Bakri, the former economics student Ghaith had met on his journey into Aleppo.

>>Abu Bakri knows what he is doing.

He is one of those very, very cool-headed, experienced commanders, and he is very methodical in the way he fights his battles.

>>(translated): This is a bomb to destroy a tank.

It's hollow on this side and blows out here.

We plant it in the roads because we don't have the bombs to match what they have.

We make them by hand.

Like these, small or large, according to the target-- anti-tank, anti-personnel or against buildings.

We make the bombs.

>>NARRATOR: Abu Bakri and his men advanced into no man's land.

They wanted to establish the location of the Syrian army's most forward position.

>>NARRATOR: Some of the fighters believed they should go no further.

But Abu Bakri sensed the tide was turning, that the government was pulling back.

(explosion) >>NARRATOR: The rebels moved forward.

>>NARRATOR: They'd fought in this district before, and knew a route that passed through abandoned houses.

The families who'd lived here had fled in a hurry, abandoning their possessions.

>>NARRATOR: Abu Bakri and his men now occupied a position they'd retreated from a few days before.

Through the barricade, they spotted soldiers in the burning house.

The Syrian army had pulled back.

>>(translated): Currently we control this line.

We're trying to advance further into Salahuddin, or the parts of Salahuddin we've lost.

If we stay optimistic and work hard in the field and on the ground, we'll advance, not them, God willing.

Losing is not an option for us.

They will lose.

We're trying to regain the areas we lost, God willing.

>>The biggest question is why the government soldiers are incapable of taking back these streets and neighborhoods.

I think they've been stretched to the limit, and we saw it.

>>NARRATOR: Ghaith returned to rebel headquarters.

The fighters had just arrested this man and claimed he was a spy.

>>A man comes to checkpoint, he blunders, he thinks that he reached the army checkpoint, so he starts praising the government.

He made a huge mistake.

>>From the bus we were allowed to film him.

He was treated very well in front of the cameras.

Then he was taken by two rebels into a room on the side of the road.

It was a horrific scene.

I saw them wrapping a gun, a Kalashnikov, around his feet.

His feet were put up, they made a stick out of wires and they start beating him on the soles of his shoes-- the falaqa, the notorious way of torturing detainees in the Syrian government.

I saw them putting a bayonet on the back of his neck, one man standing on his back, two others pulling his hands, so twisting his back.

I wonder, is it revenge?

Is it because they've been tortured themselves so hard, because they have lost friends and relatives and they are living under shelling, they become basically like the monsters they are trying to topple.

>>NARRATOR: The next day, outside headquarters, Syrian troops had suddenly reappeared.

>>They believed that this whole morning, Salahuddin was theirs.

They've took Salahuddin.

And then suddenly there was shooting coming from down that street, coming from Salahuddin area.

The same thing happened on the other end of the city.

>>NARRATOR: Abu Mohammed met commanders from other parts of Aleppo to strategize.

For Ghaith, the meeting was a glimpse into the divisions in the rebel movement.

The other two commanders are Islamists, while Abu Mohammed is secular.

>>They are cooperating because they are fighting a common enemy.

They can't afford to question where they are at this moment.

Each of them complains about the other, and at one point there will be a clash between these two forces.

>>Takbir!

>>Allahu Akbar!

>>Takbir!

>>Allahu Akbar!

(chanting) >>NARRATOR: One of the Islamists, Sheikh Abdul Rahman, showed us the streets in Salahuddin that his fighters had managed to reoccupy.

(tires squealing) He said a few days earlier, the Syrian army had destroyed this apartment complex.

His men hadn't been able to rescue the civilians trapped alive in the rubble.

One of the sheikh's lieutenants led us to another front line in the battle.

>>What was a popular uprising, activists, demonstration, calling for freedom, democracy, is now a vicious war.

The quagmire of the Syrian revolution is portrayed in the streets of Aleppo.

>>NARRATOR: The body of a local imam lay just beyond the rebel position.

>>NARRATOR: A government sniper had the street in his sights.

>>NARRATOR: A fighter tried to rescue the body.

>>NARRATOR: Eventually, he crawled into danger.

The imam's shopping bag was by his side.

He had just bought milk for his family.

The battle for Aleppo remains in the balance.

Its outcome, and the future shape of the uprising, will be decided street by street, house by house.

>>Coming up next on this special edition of Frontline, how is Bashar al-Assad holding on to power?

>>The Iranians are going to very great lengths to keep this regime together.

>>And what happens if he falls?

>>The potential for it to turn into a very dark and tough ethnic, sectarian fight is very high.

>>"The Regime Responds" isnext.

>>NARRATOR: In Syria, there is no Arab Spring.

(automatic gunfire) Here, there have been no concessions.

(explosion) As many as 20,000 people have been killed in the fight to depose President Bashar al-Assad, with no end in sight.

The story of what's happened in Syria began here 18 months ago, as change swept across the Arab world.

In a small farming town south of Damascus, a group of young schoolboys sprayed messages on these walls.

>>They were copying what they'd been listening to in Al Jazeera and other TV channels covering the Egyptian uprising and the Tunisian uprising.

>>NARRATOR: The boys were rounded up by the government's secret police, the Mukhabarat.

Their fathers went to see the police chief, a cousin of Bashar al-Assad, and begged him to release their children.

>>He refused.

And he said, "Forget that you have these kids.

Go and make other ones."

>>And if they were not men enough to make children, then, "Bring us your wives, and we will make children for you."

>>NARRATOR: Images of one boy circulated on YouTube.

>>Several of the children had their fingernails pulled out.

They were beaten.

And there were even reports of rape being committed against these children.

And in a close-knit tribal society like that, there was only one thing they could do.

>>That very instance of repression, of torture, seemed to galvanize the town itself.

Here were the children of the town being mistreated by a government that was distant, that had neglected Deraa.

And almost from that moment, the uprising seemed to gained momentum.

>>NARRATOR: At first, in rural towns like Homs, Latakia and Hama, workers and farmers were timid in their demands.

(men chanting) >>People were asking for dignity.

They were asking for housing, subsidized heating fuel.

"We want jobs.

We want cheap bread."

(chanting) >>The government was taken by surprise.

Just weeks before, President Bashar al-Assad had predicted that Syria was somehow immune to what's been called the Arab Spring, but obviously, that was not the case.

And when the uprising did erupt, there was a wave of repression, a wave of crackdowns.

(shouting, screaming, gunfire) >>It is only when the authorities turned brutal on them, deadly, that they began to chant that they want a change of regime.

>>NARRATOR: Outside Damascus, the calls for President Assad's resignation spread.

>>People in Dara'a started calling out for Homs, Homs started calling out for Idlib.

And so the more they were killings, the more solidarity was created among the Syrians.

The regime was trying to... to crush the protest movement, but in fact what they were doing is that they were spreading it even more.

>>NARRATOR: But Bashar al-Assad was convinced he had wide enough support.

>>There's still a lot of Syrians who are very loyal to the regime and frightened of the countryside getting too much power and taking over and perhaps being too fundamentalist and other things for them.

>>NARRATOR: In Damascus and Aleppo, government workers and regime supporters were sent into the street to rally for the president.

>>There are many people that do very well by the Assad regime-- minorities in Syria, Alawites, Ismaelis, Druze, members of the Sunni bourgeoisie, in Damascus in Aleppo.

So they serve as the backbone of the regime.

>>NARRATOR: It had been a month since the uprising began when President Assad came before parliament.

Syria's business and political elites showed that they were behind him.

>>He walked in and it was all very jovial.

There was a lot of clapping and cheering every time he spoke.

At one point, one of the members of parliament stands up and says, "Sire, you are such a brilliant leader that you should not just be the leader of Syria, you should be the leader of the world."

>>The expectation-- not only the popular expectation but the expectation of those circles of power-- were that Bashar al-Assad was going to stand there and introduce a package of reforms that, hopefully, would allay these grievances and would meet with the popular demands.

Instead, he stands up there to accuse this entire uprising of being a foreign conspiracy.

>>There was no sense of remorse.

That's what shocked people.

There seemed to be a complete detachment, as if, "Everything's going to be okay.

"My people love me.

"And look, my car was being mobbed as I leave the parliament."

(applause) >>NARRATOR: The Assad family belong to a minority Shia Muslim sect, the Alawites, that for decades have controlled Syria's military and security forces.

They were not about to let their power slip away.

>>They have their backs against the wall.

The Alawites, who are about two million people, feel that when they lose, and if they lose, they're going to be cast out.

It'll be like the Sunnis in Iraq, who were cleaned out of every major government agency.

>>Over time, Bashar al-Assad was successful in convincing the majority of the Alawites that his political survival is synonymous with their physical survival.

And they have started seeing this fight in existential terms.

>>It's very understandable why Alawites would believe today that if they were to lose, they would lose more than the privileges that the regime has had.

They would lose everything.

>>NARRATOR: The Alawites' improbable rise to power in Syria was set in motion by Bashar's father, Hafez al-Assad.

His path to power was through the military, which was dominated by Alawites.

A rising star in Syria's Socialist Ba'ath Party, at age 40, he engineered a coup to seize the presidency.

>>Hafez al-Assad rose to power from the bottom up.

He had to fight the battles that came with the coup d'états, that came with trying to corral the different forces of the country into his camp.

>>He knew he had to gain support of the other minorities-- the Druze, the Christians, the Shiites.

So he said, "I'm a minority entity.

You want to be with me because my interests are your interests."

>>NARRATOR: Hafez al-Assad secured his power by putting trusted family members in high government posts.

>>The brother is in charge of security, the cousins of the banking system, in-laws in security as well, and military.

So the reality is, this is a family business.

>>NARRATOR: Like Saddam Hussein in Iraq, Assad's Ba'ath Party repressed any ethnic or religious challenges.

>>The Ba'ath Party promised to get rid of sectarianism.

He demanded, and for the most part the Syrian population was receptive to, this Faustian bargain that the Syrian people would accept less freedom and liberty in return for stability.

>>NARRATOR: He took in millions in Soviet military aid and formed an alliance with Iran, which still endures.

>>The relationship with Iran is very unusual.

Syria is a secular state ruled by a secular Arab Nationalist party, the Ba'ath Party.

Iran is an Islamic republic.

So they don't seem to be a marriage made in heaven.

But it's a symbiotic relationship that's based on strategic necessity.

>>It's not a particularly natural alliance, if you will.

But for reasons of common enmity towards Iraq, towards Israel and other regions, they did form this alliance that has been the strongest, the most enduring in the region.

>>NARRATOR: But back in the early 1980s, while Assad was building an alliance with the new Shiite theocracy in Iran, he was facing resistance from fundamentalist Sunnis at home.

>>There was a very aggressive Islamic fundamentalist opposition to the Syrian regime.

There were attacks against the regime.

It was essentially almost a civil war.

(explosions) >>NARRATOR: The Assad regime's response was to attack the stronghold of Syria's Muslim Brotherhood, the town of Hama.

>>In 1982, the Syrian regime launched one of the worst massacres in the history of the Middle East.

The regime used artillery to level large parts of the town.

Between 10,000 and 30,000 people were killed or were disappeared.

>>That was a very stark moment in which the Alawite-dominated regime, the Ba'ath Party, made it clear to Syria that it would not brook any opposition.

>>It was a ruthless, obviously Machiavellian way to deal with the problem, but it did deal with the problem from the perspective of the Syrian regime, because until recently, you really haven't had any serious Islamist opposition to Hafez al-Assad or his son when he came to power in 2000.

>>NARRATOR: Bashar was never supposed to be heir apparent.

But his older brother, Basil, was killed in a car accident in 1994, and Bashar was ordered to come home from his medical studies in London, to be prepped for the day he would take office.

>>We all knew he was going to take over.

We all knew that Hafez al-Assad was on his last legs, if you want.

You know, he was close to death.

It was very clear that he was very ill. And the question was always, how well groomed has Bashar been?

>>NARRATOR: He was inaugurated in July 2000.

The young doctor, with his fashionable British-born Syrian wife, a former banker at JP Morgan, promised reform.

>>People were giddy with the idea of reform early on in Bashar's reign.

He opened up the country to the Internet.

He lifted exit permits, which were required for Syrians to travel, and he allowed more trade in the country.

>>He said, "We can open up.

We are going to have some private newspapers, private press, Internet."

And he believed that he could win the hearts and minds of the people through modernization and let a lot more light in.

>>He had allowed what came to be known as the "Damascus Spring."

He promised reforms, and he promised political reforms.

And so people began to talk about ideas.

How is Syria going to meet the future?

Which path is it going to take?

And there was an era in which there was an open debate, and a healthy one.

>>He was genuinely popular amongst the young people, who hadn't lived through his father and who saw him as a potential reformer.

And he kept on telling them that life is going to get better.

And they could see fairly dramatic changes, at least for the wealthy.

>>NARRATOR: It didn't last.

Hundreds of activists and intellectuals were arrested.

>>The political establishment, the Ba'ath Party, decided that if this free political debate was going to continue, they were going to lose their heads.

And so it was the return of authoritarianism.

>>NARRATOR: The Damascus Spring was over.

Six years later, another spring.

When news of the successful revolts in Tunisia and Egypt spread, the long-oppressed Sunni majority believed their time had finally come.

In largely peaceful demonstrations across the country, Syrians defied their president, in spite of increasingly brutal attacks by the police.

The center of resistance was the town of Hama, where Bashar's father had famously crushed a Sunni rebellion almost 30 years earlier.

>>The regime has a playbook.

If you're faced with a crisis, go back to the playbook and see what we did the last time we got through a crisis.

So the last time they got through a similar crisis was Hama.

So you have a protest.

You have an uprising.

You suppress it.

The playbook does not say negotiate with the protesters, so there's no negotiation.

>>That one very high-ranking Turkish official told me that what's going on inside the leadership is that Bashar's mother herself is telling him that these are the same events, that they remind her of what happened in the late '70s and early '80s.

And her advice to him is that he has to act like his father.

He has to be strong, he has to be decisive, and he has to crush this element of rebellion against him.

>>NARRATOR: Bashar sent in tanks, armored vehicles and snipers.

>>This is how the Assads, both father and son, deal with domestic threats.

They retreat into their Alawite fortress, and there's this convulsive reaction to put down any sort of domestic threats, and to put them down ruthlessly.

>>NARRATOR: But even then, some in the leadership questioned whether Bashar was tough enough.

>>In some quarters, there was talk of the fact that your father was much harsher, he would have used more force, he would have rooted all this out right from day one.

You were too lenient on them.

>>There were calls at the time inside the Alawite community of saying, "We don't want Bashar, we want Maher," who is Bashar's brother.

He's the leader of the Republican Guard, of the Fourth Armored Division, which is the most ruthless.

And I think that's the time then when the decision has been made by Bashar and by the people around him that they need to up their game in terms of meeting the rebel movement.

(explosion) (shouting) (explosion) >>NARRATOR: This February, to show his resolve, Bashar al-Assad moved on the country's third largest city, Homs.

>>Homs has been an epicenter of opposition to Assad.

And so he wanted to send a lesson to the rest of Syria that he can turn their cities into rubble if they oppose him.

>>NARRATOR: Homs endured 30 straight days of shelling.

Most of the artillery was trained on the predominantly Sunni neighborhood of Baba Amr.

>>You look at Baba Amr today, and it's... it looks like a Stalingrad.

You know, it's just entire, you know, streets are just flattened.

>>Until Baba Amr, there was a belief inside the opposition ranks that the nonviolence movement that worked in Tunisia, that worked in Egypt, could still work in Syria.

Baba Amr was the beginning of the shift.

After that, people were starting to call for jihad, jihad.

(explosion) (repeated gunfire) >>There's been a shift, not just in terms of what the opposition was willing and able to do, but also in terms of what the regime was willing to do now.

And we see, then, an continuing escalation.

>>NARRATOR: In May, more than a hundred people, including dozens of children, were brutally massacred in a Sunni village in Houla, the work of Alawite paramilitaries.

>>This was the first massacre to come to light as it was happening.

And a lot of people were saying, "Oh, well, this is the one that's going to bring the international community to support us," you know.

"Because now they've crossed the red line."

And unfortunately for Syria, even a massacre like Houla did not bring enough response beyond the usual round of condemnations and sanctions.

>>NARRATOR: But President Assad blamed the massacre on outsiders.

He rejected UN efforts to intervene.

>>(on TV): Breaking news coming out of the capital, the defense minister has been killed in a suicide attack... >>(on TV): A bomb ripped through the heart of President Assad's... >>(on TV): An explosion that may have changed Syria's future.

>>NARRATOR: In July, a brazen bomb attack in the center of Damascus killed a group of Assad's most trusted military advisers.

>>That was a very severe blow for the regime.

They lost some of their most experienced coordinators of the campaign being run against the opposition.

>>That is the minister of defense.

That is the national security adviser.

And that is, first and foremost, his brother-in-law, the chief of military intelligence.

And here, the beast has lost his eyes.

And here the regime went berserk.

(explosion) >>NARRATOR: The battle for Syria became the battle for Aleppo.

The Free Syrian Army had made a fateful decision to pull their forces from other areas, to try to take control of the country's biggest city and business center.

(automatic weapons fire) (shouting) >>NARRATOR: President Assad responded.

>>The regime now is bombarding civilian neighborhoods with artillery, with tank fire, and now with helicopter gunships and with fighter bombers, using MiG-21 and MiG-23 interceptors to shoot at civilian neighborhoods, to shoot randomly at apartment buildings.

And in the past few days in Aleppo, these MiGs have shot at people who were waiting in a bread line.

This is how desperate I think the regime has gotten.

>>NARRATOR: For now, the battle for Aleppo seems at a stalemate.

But other players are attempting to tilt the balance.

Syria's longtime ally, Iran, is providing weapons and training to the Alawite paramilitary forces.

>>The Iranians are gaining influence in Syria now by the day.

I mean, watching this happening, like what they did in Iraq in a very sophisticated, very smart way.

They used to provide strategic advice to Assad regime.

Nowadays, they are even leading operations.

>>NARRATOR: Opposing Iran is Saudi Arabia, which is backing the Sunni rebels.

>>The rivalry between Saudi Arabia and Tehran had started long before the Syrian uprising.

And now with the Syrian uprising, the Saudi government saw this as an opportunity to deal a mortal blow to Iran.

And they have carved that niche in this conflict by sending weapons and money to the rebels.

(chanting) (explosion) But as long as they have the Iranian support, I think this regime can continue to fight for some time.

>>The potential for it to turn into a very dark and tough sectarian fight, the way it did in Lebanon and Iraq, is very high.

And the regime has made it very clear that, "We're not going anywhere.

"And we're going to fight to the end.

"And if you want to take us on, you have to be prepared to sacrifice everything, and you may not win."

It's hard to see where this ends.

(gunfire) >>Frontline continues online with more from Guardian reporter Ghaith Abdul-Ahad on his journey into the front lines of the fight.

>>We are withdrawing now, after the attack.

>>Explore the critical hubs of the Syrian rebellion in our interactive map.

Hear from experts on the long-term consequences of this conflict.

Watch the program online, and follow Frontline on Facebook and Twitter, or tell us what you think at pbs.org/frontline.

>>For more on this and other Frontline programs, visit our website at pbs.org/frontline.

Frontline's "Battle for Syria" is available on DVD.

To order, visit shoppbs.org or call 1-800-PLAY-PBS.

Frontline is also available for download on iTunes.