Updated

Activists are reporting heavy fighting in northern Damascus neighborhoods as troops try to advance against rebel forces.

The Britain-based Syrian Observatory for Human Rights says the fighting between rebels and troops backed by pro-government militiamen are concentrating in Jobar and Barzeh.

The Local Coordination Committees, another activist group, said troops bombarded the nearby neighborhood of Qaboun on Friday with mortars and multiple rocket launchers. No one gave casualty figures.

Government forces have been on the offensive for days in and around Damascus in an apparent attempt to secure President Bashar Assad's main stronghold against rebel challenges.

Syria's conflict started with largely peaceful protests against Assad's regime in March 2011 but then turned into a civil war.

More than 70,000 people have been killed, according to the United Nations.