Syrian activists say government aircraft pounded opposition strongholds on the outskirts of Damascus while troops clashed with rebel fighters in several other areas of the country Sunday, leaving a U.N.-backed truce declared for the Muslim holiday of Eid al-Adha largely in tatters.

Amateur videos posted on YouTube appeared to support claims of the Britain-based Syrian Observatory for Human Rights that government airstrikes hit the capital city suburbs of Irbin, Harasta and Zamalka.

The Observatory and another activist group, the Local Coordination Committees, said government troops also shelled those areas in an attempt to drive out rebels.

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 fighting Sunday comes on the third day of what was to be a four-day holiday cease-fire between the government and rebels.

It was to begin on Friday, but 150 people were killed that day. On Saturday, about 50 people were killed. The number of casualties Sunday was immediately clear.

U.N. special envoy Lakhdar Brahimi arranged the cease-fire so Syrians on all sides could celebrate Eid al-Adha, the holiday marking the end of the annual Muslim pilgrimage to holy sites in Saudi Arabia.