An estimated 600 Free Syrian Army fighters were involved in a simultaneous attack on government targets from five directions around the capital Damascus, Sky News has learned.
During the operation on Friday night a bus carrying Russian oil workers was hit and rocket-propelled grenades were fired at a building that was housing them.
A civilian Syrian woman is said to have been killed in the attack on the building.
From information given to Sky News by people living in some of the districts it appears the attacks were co-ordinated.
They began at 1pm and continued until 5pm. After a two-hour lull the fighting began again in all areas at 7pm and continued until around midnight.
An electricity power station was hit as the attacks took place in Daria, Mleha, Ghorba, Kfe Sosa and in the Mezzah area closer to the city centre.
Our sources say many of the fighters, some wearing uniforms, were captured or killed.
We do not know if there were casualties on the government side - the authorities here are not speaking on the record about the incident.
One source said "several Russian oil experts" died and others were injured, but there is no confirmation of this.
Russian fatalities have not been reported by either the Syrian or Russia media.
Eyewitnesses say they saw ambulances leaving the scene but no one could confirm if Russians had indeed died.
There are thousands of Russians in Syria, mostly technical experts working here accompanied by their families.
During Friday night's fighting a Sky News team drove past some of the areas in North Damascus which were under attack. A huge plume of smoke rose above one district.
At what is a normally quiet checkpoint, dozens of cars were backed up along both lanes of the highway. Extra security was apparent and lorries were being searched with more care than usual.
We were twice diverted from the usual route into town by army roadblocks. I saw one tank taking up position on a flyover bridge and heard two bursts of machine gun fire.
Later, at the TV station, the Sky team saw troops being reinforced at the entrance.
We heard later that the government believes Friday's attack was by far the biggest and most organised on the capital so far and were concerned that key facilities in the city centre might also be hit.
Privately they appear satisfied that the security forces were able to deal with the offensive.
The incident is probably a sign of things to come. Both sides will have learned lessons for the next time.