Updated

Syrian warplanes carried out airstrikes on a suburb of the capital on Thursday after talks for a two-week truce between the government and rebels collapsed, anti-government groups said.

The Local Coordination Committees and the Britain-based Syrian Observatory for Human Rights said the airstrikes struck the rebel-stronghold of Douma, inflicting casualties.

The airstrikes came after the Observatory said indirect talks for the truce between the opposition and representatives of President Bashar Assad's government collapsed after rebels refused to release prisoners.

The negotiations aimed to achieve a two-week cease-fire in the suburbs of Damascus known as Ghouta, where fighting has been ongoing since 2012. The truce was supposed to begin on Thursday morning.

Opposition activist Hadi Abdullah wrote on Twitter: "The Assad regime killed the truce before it was born."

Abdurrahman said the indirect negotiations, being handled by an unnamed third party, ended because of disagreements over how much food and medicine should enter Ghouta. The government also wanted all members of Assad's Alawite sect who are held by Islam Army be released, he said.

A third point of disagreement was that the rebels wanted the ceasefire to cover all parts of Ghouta, but the government insisted that it only include the suburbs of Harasta and Douma, Abdurrahman said. He said the negotiations have been ongoing for days.

Ghouta is a stronghold of the Islam Army rebel group, one of the strongest factions in Syria's conflict. Islam Army spokesman did not respond to calls seeking comment.

The ceasefire talks come amid intensified international efforts to bring an end to the Syria crisis, which has killed more than 250,000 people since March 2011. A meeting in Vienna last week involving nearly 20 foreign ministers set a Jan. 1 deadline to start negotiations aimed at achieving a transitional government and eventually elections.