By nearly all measures, Lebanon should have long ago buckled under the weight of Syria's civil war.

The fighting next door has swamped Lebanon with refugees and has stoked its Sunni-Shiite tensions, as each community in Lebanon lines up in support of its brethren on the rival sides in Syria. That has fueled predictions that deeply divided Lebanon is only one nudge away from collapsing into full-blown sectarian bloodletting of its own.

Yet, 2 ½ years into Syria's war, Lebanon is still standing — barely. One reason is Lebanon's memory of its own traumatizing 15-year civil war. Another, related reason is the internal balance of fear that underpins the country's ramshackle political system: Each faction and sect is restraining its followers, well aware that the slightest mistake could bring the house down around everyone.

"I think most of the doomsayers have proven to be wrong about Lebanon descending into all-out war, but the situation is very dangerous, very grim, very fragile indeed," said Fawaz A. Gergez, director of the Middle East Center at the London School of Economics.

The question is how much stress that system can bear and for how long. Lebanon, a country of 4.5 million people, has taken in more than 1 million Syrian refugees, straining its resources. A string of deadly bombings and sectarian gunbattles linked to Syria has killed more than 120 people and wounded hundreds more. There has been no functioning government since April because of political divisions over Syria. Parliament, meanwhile, has unilaterally extended its own mandate by 18 months by skipping scheduled elections.

On top of everything, Lebanon's strongest political, social and military force, the Shiite militant group Hezbollah, is openly fighting alongside Syrian President Bashar Assad's troops in Syria, while Lebanese Sunni militants have taken up arms with Syria's predominantly Sunni rebels against Assad.

The danger for Lebanon zoomed into focus again Tuesday when a double suicide bombing targeting the Iranian Embassy in Beirut killed 23 people and wounded more than 140 in a mainly Shiite district of Beirut.

An al-Qaida-linked group claimed responsibility for the attack, and called it payback for Hezbollah's support for Assad against the predominantly Sunni rebels. Iran, the regional Shiite power, is a key supporter of Hezbollah and the Syrian government.

The bombing was the fifth this year in Lebanon tied to the Syrian war. In Lebanon's second-largest city, Tripoli, bloody street fighting between mainly Sunni opponents of Assad and mainly Shiite and Alawite supporters has become a near-weekly affair, the latest of which killed at least 17 people and wounded around 80.

Each incident of violence sparks fears that the targeted community will lash out dramatically at the rival community, triggering an unstoppable cycle of violence. This was particularly true after an explosion in a Hezbollah stronghold south of Beirut killed 27 people in mid-August, followed less than two weeks later by a double bombing outside Sunni mosques in Tripoli that killed nearly 50.

For days after, Lebanon's political talk shows, newspapers and cafe conversations were filled with talk of Iraqi-style retaliatory bloodshed.

Yet, Lebanese did not take up arms and rush to the barricades. Very few people, regardless of sect, want to head back down a dark path reminiscent of Lebanon's 15-year war. That conflict, which ended in 1990, pitted the country's faiths and ethnic groups against each other, killed 150,000 people, destroyed Lebanon's infrastructure and economy and turned the capital, Beirut, into a shattered wreck of its former glamorous self.

"I honestly thought people would take to the streets by now and fight each other based on sects ... but I think that after our experience with the civil war, we became slightly smarter than to allow ourselves to get sucked in," said Marah, the owner of a clothes boutique in the Druse town of Baakline.

"We know that sectarian tensions will always be under the surface. So far, it's been relatively under control but I'm scared that another spark from Syria will have the country explode," she said, speaking on condition she be identified only by her first name because of a reluctance to talk about sectarian issues publicly.

The country's politicians are acutely aware of its potential to be torn apart at its many seams. The bosses of Lebanon's sectarian communities — Sunni, Shiite, Christian and Druse — have so far been able to restrain tempers.

After Tuesday's suicide bombings, Hezbollah's deputy chief, Naim Kassem, urged calm and called on politicians to clear the air of "sectarian and ethnic toxins" Asked whether Lebanon was going the way of Iraq, he said, "We are still in the beginning of the road and we can deal with it if there is the proper will."

Because of its political clout and heavily armed militia, Hezbollah has played a key role in keeping a lid on the violence. The group boasts the best equipped and best trained fighters in Lebanon, outstripping even the national army.

Hezbollah's rivals may be infuriated by its intervention in Syria and by its political domineering at home, but none of them wants to challenge it on the streets.

"Let me be blunt — who is going to take on Hezbollah in Lebanon?" said Gerges of the London School of Economics. The group's enemies, he added, "realize that Hezbollah can exact a great deal of damage."

Hezbollah leader Hassan Nasrallah, in turn, knows that if serious sectarian fighting did erupt, many would place the blame squarely on Hezbollah's shoulders for sending thousands of fighters to Syria. Nasrallah has publicly called for Lebanon to be spared any fighting, saying rivals should go fight in Syria and keep Lebanon out if.

"Hezbollah will not allow itself to be entrapped, to fall prey to waging battle inside Lebanon," Gerges said. "Nasrallah will not fire the first shot, will not provide the spark, will not allow himself and his party to fall prey to an all-out war in Lebanon."

So that leaves Lebanon hanging just on the edge, with Lebanese worrying about if and when it will tip over it.

"It's very simple, you play with fire, you get burned. If we keep meddling in Syria, whether supporting the regime or the rebels, it's going to backfire," said Basil, an electronics merchant who lives in Shiite neighborhood of Jnah in Beirut. He spoke on condition he be identified only by his first name because of worries over talking publicly about sectarian issues.

"One bombing will lead to another as retaliation. One bullet fired on sectarian basis will lead to another. We can't afford to relive a civil war"


Associated Press writer Yasmine Saker contributed to this report.