More than 305 people were killed across Syria on Wednesday, making it the bloodiest single day of the 18-month revolt, the Syrian Observatory for Human Rights said.

"This is the highest toll in a single day since March 2011. And this is only counting those whose names have been documented. If we count the unidentified bodies, the figure will be much higher," Observatory director Rami Abdel Rahman told AFP by telephone.

A total of 199 of Wednesday's dead were civilians, the Britain-based watchdog said.

In the eastern city of Deir Ezzor, 23 people, including a child and a woman were killed by army gunfire when troops stormed the Jura district.

In Damascus, 17 people, including eight women and three children, were shot dead in the northern Barzeh neighbourhood, the watchdog said.

Another 14 people were killed when two bombs struck the Syrian army headquarters in the heart of Damascus, according to the Observatory.

Outside the capital, 40 bodies, including those of women and children, were found in the village of Diabeya.

The previous highest death toll of the uprising was on July 19, when 302 people were killed, according to the Observatory.

More than 30,000 people have been killed in violence since the outbreak of the revolt against the rule of President Bashar al-Assad in March last year.