More than 19,000 people have been killed in violence in Syria since the outbreak of an anti-regime revolt last year, the Syrian Observatory for Human Rights said on Sunday.

"At least 19,106 people, most of them civilians, have been killed since March last year," the Observatory's Rami Abdel Rahman told AFP.

They included 13,296 civilians, 4,861 regime troops and 949 defectors, he said, noting that the civilian toll included people who had taken up arms against the regime.

"The toll does not include the thousands of people missing in detention," said Abdel Rahman. "Nor does it include thousands of soldiers whose deaths the regime has concealed, in a bid to keep the army's morale high."

It is impossible to independently verify death toll accounts from Syria.

The Observatory's latest count was released as regime troops stormed the Barzeh district of Damascus on Sunday, and as fighting engulfed neighbourhoods of Syria's second city Aleppo.

"Barzeh is being stormed by the feared Fourth Brigade" headed by President Bashar al-Assad's brother Maher, Abdel Rahman said, noting that dozens of neighbourhood residents were fleeing the area as helicopters pounded it and snipers were deployed on the district's rooftops.

"The deployment in Barzeh is very heavy," Abdel Rahman added.

Regime forces also deployed in the outskirts of the Mazzeh district of the capital, he said, adding one person was killed there on Sunday and several were wounded.

Elsewhere, clashes engulfed several districts of Aleppo, scene of heavy fighting since Friday. Violence was reported around the Salaheddin and Sakhur districts, Abdel Rahman said.

The army's assault on Salaheddin began at dawn, in a bid to reclaim it from rebel hands, an anti-regime activist told AFP.

"Violent clashes have been taking place since the early morning," the activist said on condition of anonymity.

A total of 164 people were killed in violence across Syria on Saturday, including 86 civilians, 49 soldiers and 29 rebel fighters.

Of those killed on Saturday, 27 civilians died in the embattled central province of Homs, including two women and six children in the rebel-held town of Rastan, which regime forces have shelled violently for several months.

In Damascus, those killed included a senior army general and weapons expert, assassinated by "unidentified gunmen" alongside his wife and two children in the historic district of Bab Touma, according to the Observatory.