Syrian activists say government aircraft pounded opposition strongholds on the outskirts of Damascus and 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's Sunni Muslim suburbs of Irbin, Harasta and Zamalka.