Observatory director Rami Abdurrahman said the rebels were trying to open the road between Ghouta and the outside.
He said more than 160 fighters were killed on Friday and Saturday, including nearly 100 rebels, most of them from al-Qaida-linked groups, the Nusra Front and the Islamic State of Iraq and the Levant.
Among the more than 60 fighters killed on the government side were 20 gunmen from the Iraqi Shiite Abu al-Fadl al-Abbas brigade, he said.
Abdurrahman bases his information on a network of activists on the ground, as well as employees of military hospitals who fill him in on army casualties.
