Heavy clashes broke out between Syrian government forces and insurgents east of Damascus on Monday when troops tried to reach under the cover of a dozen airstrikes a force trapped inside, opposition activists said.
The clashes have been ongoing for three days but on Sunday, rebels backed by al-Qaida-linked fighters attacked troops and pro-government gunmen capturing parts of a military installation and surrounding a force inside.
The Britain-based Syrian Observatory for Human Rights and Syria-based activist Mazen al-Shami said Monday's fighting was concentrated inside the military installation near the suburb of Harasta, where the government force has been trapped.
The Observatory said the Syrian air force conducted at least a dozen airstrikes on Harasta and nearby suburbs. Al-Shami reported dozens of airstrikes. He said the government brought in reinforcements overnight and is trying to reach the trapped force.
The Observatory said three days of violence in the suburbs of Damascus known as eastern Ghouta has killed 35 civilians, as well as 24 government troops and 29 insurgents.
An official with the ultraconservative Ahrar al-Sham insurgent group said the government is negotiating the passage of its fighters trapped in the military installation. The official, who asked not to be named because of the secrecy of the talks said the negotiations are in their preliminary stages.
Syria's state media did not mention the trapped force but blamed insurgents for the violence saying that they are firing shells into government-controlled areas killing at least one civilian.
The U.N. says government forces are holding nearly 400,000 people under siege in eastern Ghouta. The region was once a hotbed of protest against President Bashar Assad's government.