The Syrian Observatory for Human Rights had reported on Sunday the discovery of 320 bodies in Daraya after what opposition militants said was a brutal onslaught of shelling, summary executions and house-to-house raids by government troops.

The Observatory said another 14 bodies had been found on Sunday, and that it had so far identified 220 of the dead.

The Local Coordination Committees -- a network of activists on the ground -- described the killings as a "massacre" by the regime of President Bashar al-Assad.

The Britain-based Observatory said at least 149 people were killed across the strife-torn country on Sunday, among them 105 civilians, 26 rebel fighters and 18 soldiers.

Regime forces shelled Basra al-Sham in the province of Daraa, cradle of the 17-month uprising, killing at least 17 civilians on Sunday, it said.

"Among them were women and children," said the Observatory, which has a network of sources on the ground including doctors and activists.

New shelling on Monday killed three men, three children and two women in Kafr Batna in the province of Damascus, the Observatory added.

Around 25 000 people – most of them civilians – have been killed in Syria since the outbreak of a revolt in March last year turned into a bloody insurgency after the regime launched a massive crackdown on dissent, according to Observatory figures.

It is impossible to independently verify death tolls reported in Syria because of severe restrictions on media operating there.