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Associated Press
In this Saturday, Oct. 27, 2012 photo, a rebel fighter runs for cover through a sniper line-of-fire, in the southeast area of Aleppo, Syria. (AP Photo/Narciso Contreras).

BEIRUT — Syrian warplanes and artillery struck rebellious suburbs east of Damascus, while rebels attacked regime positions elsewhere near the capital Sunday, violence that marred the third day of what was meant to be a four-day holiday truce, activists said.

A U.N.-backed truce declared for the Muslim holiday of Eid al-Adha has failed to take hold, with fighting reported from the start. Activists said more than 150 people were killed Friday, the start of the holiday, and more than 120 people on the second day, similar to previous daily casualty tolls.

The cease-fire was seen as a long shot from the outset. The international mediator in Syria, Lakhdar Brahimi, failed to get firm commitments from all combatants.

At least one rebel-linked radical Islamic group, the al-Qaida-inspired Jabhat al-Nusra, rejected the truce outright. In a video posted this week, the leader of al-Qaida, Ayman al-Zawahri, urged "Muslims everywhere" to support Syria's uprising.

The truce was called as the two sides were battling over strategic targets in a largely deadlocked civil war. They include a military base near a main north-south highway, the main supply route to Aleppo, Syria's largest city, where regime forces and rebels have been fighting house-to-house. It appears each side feared the other could exploit a lull to improve its positions.

With the unraveling of the cease-fire, it's unclear what the international community can do next.

The holiday truce marked the first attempt in six months to reduce the bloodshed in Syria, where activists say more than 35,000 people have been killed in 19 months.

Brahimi has not said what would follow a cease-fire. Talks between Syrian President Bashar Assad and the Syrian opposition on a peaceful transition are blocked, since the Syrian leader's opponents say they will not negotiate unless Assad resigns, a step he has refused to take.

The international community has been unable to rally around other options, including tougher U.N. Security Council action, arming the rebels or direct military intervention.