Karin Laub

BEIRUT: A Syrian warplane flattened a three-story building, suspected rebels detonated a deadly car bomb and both sides traded gunfire in several hot spots across the country Saturday, activists said, leaving a U.N.-backed holiday truce in tatters on its second day.

The unraveling of the cease-fire marked the latest setback to ending Syriaís civil war through diplomacy. Foreign military intervention is unlikely, raising the grim prospect of a drawn-out war of attrition between President Bashar Assad and those trying to topple him.

The proposed four-day truce during the Muslim holiday of Eid al-Adha had been a long shot from the start since international mediator Lakhdar Brahimi failed to get solid commitments from all combatants. Fighting dropped off in the first hours of the cease-fire Friday, but by the end of the day, activists said 151 people had been killed in bombings and shootings, a typical daily toll in Syria.

On Saturday, the first regime airstrike since the start of the truce reduced a three-story building to rubble in the Arbeen suburb of the capital, Damascus. At least eight men were killed, said the Britain-based Syrian Observatory for Human Rights, which compiles reports from activists.

In the remote eastern town of Deir el-Zour, assailants detonated a car bomb near a military police compound, then opened fire at those rushing to the scene, killing a total of eight people and causing extensive damage, the Observatory said. Syrian media denied there were casualties. The attack bore the hallmarks of Jabhat al-Nusra, a radical rebel-allied Islamic group that has rejected the cease-fire.

The Syrian air force also bombed rebel positions Saturday during a fierce battle for control over the main road linking Aleppo, Syriaís largest city, with the capital, activists said. Earlier this month, rebels seized Maaret al-Numan, a town along the highway and besieged a nearby military base, disrupting regime supplies to embattled Aleppo. The Syrian air force has responded with sustained bombing raids on area villages.

By late Saturday, at least 76 people had been killed across Syria, including 20 Syrian soldiers, activists said. The Observatory reported deadly regime shelling and sniper attacks in several locations, while Syrian state-media said rebels ambushed a number of military positions.

Military analyst Joe Holliday said neither side has an incentive to halt fighting, noting that rebels have disrupted regime supply routes to the northern provinces of Aleppo and Idlib. ďThe regime canít accept the current military status quo without a fight and the rebels have no reason to since they believe they have the momentum,Ē said Holliday, a researcher at the Institute for the Study of War in Washington.

Brahimiís spokesman declined to comment Saturday on the apparent failure of his initiative. Itís not clear what Brahimiís next move could be, since the international community is divided over the Syria conflict.