Fighting in Syria's capital appears to be worsening, with reports that regime forces are using helicopter gunships and tanks to try to wrest back control of suburbs now in the hands of rebels.
Since Sunday, the fighting has slowly spread across Damascus.
Reports say helicopter gunships, fitted with heavy machine guns, strafed key neighbourhoods on Tuesday.
Several blasts shook another district a few hours after rebels had announced a full-scale offensive to take the capital.
Witnesses reported heavy machinegun fire in Sabaa Bahrat Square in the heart of Damascus. Shooting was also reported in Baghdad Street, a main road near the square.
Troops also targeted an electrical power sub-station in Qaboon, causing huge power cuts.
The (rebel) Free Syrian Army said fighting would not stop until the whole of the capital had been conquered.
The Syrian government denies the reports that there is fighting in one of the capital's main streets.