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 UN-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 ceasefire was seen as a long shot. 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-Qaeda-inspired Jabhat al-Nusra, rejected the truce outright. In a video posted this week, the leader of al-Qaeda, 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 primary supply route to Aleppo — Syria's largest city — where regime forces and rebels have been engaged in house-to-house fighting. It appears each side feared the other could exploit a lull to improve its positions.

With the unravelling of the ceasefire, 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 ceasefire. Talks between President Bashar al-Assad and the Syrian opposition on a peaceful transition are blocked, since the Syrian leader's opponents say they will not negotiate unless he resigns, a step he has refused to take.

In fighting Sunday, Syrian warplanes struck the eastern Damascus suburbs of Arbeen, Harasta and Zamalka to try to drive out rebels, according to the Britain-based Syrian Observatory for Human Rights, which compiles information from activists in Syria. The Observatory also reported shelling attacks in these areas.

Local activists and another opposition group, the Local Coordination Committees, said warplanes struck Arbeen and Harasta. The LCC said eight people were killed Sunday in Damascus and its suburbs.

Widespread destruction, shattered windows

Three amateur videos posted online showed warplanes flying over the eastern suburbs of the capital.

One video showed two huge clouds of smoke rising from what was said to be Arbeen, and the sound of an airplane could be heard in the background. It was not clear if the video showed the aftermath of shelling or an airstrike.

Another video showed destruction inside the Sheikh Moussa mosque in Harasta. Windows and doors were blown out, glass and debris scattered across the mosque's floor. The narrator broke down as he was heard saying: "Where are the Muslims? Our mosques are being bombed and no one cares."

Also in Harasta, a video showed widespread destruction, including rows of buildings with shattered windows, gaping holes and shell-pocked facades.

The videos appeared consistent with Associated Press reporting in the area.

In Douma, another Damascus suburb, rebels wrested three positions from regime forces, including an unfinished highrise building that had been used by regime snipers, according to the Observatory and Mohammed Saeed, a local activist.

Fighting was also reported near Maaret al-Numan, a town along the Aleppo-Damascus highway that rebels seized earlier this month. Opposition fighters have also besieged a nearby military base and repeatedly attacked government supply convoys heading there. The Observatory said the Syrian air force fired missiles and dropped barrel bombs — makeshift weapons made of explosives stuffed into barrels — on villages near the base.

The Syrian government has accused the rebels of violating the ceasefire from the start. The state-run news agency SANA said opposition fighters carried out attacks in a number of areas, including in Aleppo and the eastern town of Deir el-Zour.