Syrian rebels launch 'third phase' of Damascus offensive
Rebel fighters carried out a series of dawn raids from the rebel stronghold Jobar, while the regime responded with huge air raids and shelling on opposition areas.
Photos released by Syrian activists showed massive devastation to opposition areas with many civilians believed to be dead.
There have been more than 650 cases of bombing or shelling by the Syrian regime since fighting broke out in the capital on Sunday, according to the Syrian Observatory for Human Rights.
The Free Syrian Army described the new assault as the "third phase" of its operation to liberate Damascus.
This began with suicide attacks and assaults by Fatah al-Sham or Faylaq al-Rahman fighters.
The FSA said its fighters and allied Hayaat Tahrir al-Sham militants had recaptured areas lost to the regime after a counter-offensive on Monday.
Opposition activists said rebel fighters had captured the industrial zone near Jobar and were pressing on to Abbasid Square, right at the edge of Old Damascus.
The FSA also said it had cleared Islamic State group positions in the rebel-held Qalamoun area near Damascus, following days of fighting between the two sides.