At least 15 people were killed and dozens wounded on Monday in government air strikes on an area outside the capital Damascus, the Syrian Observatory for Human Rights monitor said.
There were no immediate details on the breakdown of those killed in the strikes, which are the latest to hit the town of Douma in the rebel stronghold of Eastern Ghouta.
The opposition bastion, east of Damascus, came under a massive government aerial assault on Thursday after rebels fired more than 120 rockets and mortar rounds into the capital.
The rebel barrage killed 10 people in Damascus, including a child, while the government air strikes and surface-to-surface missiles fired at Eastern Ghouta killed at least 82 people, among them 18 children.
Eastern Ghouta has been under government siege for nearly two years as the army tries to break the rebel hold over the area.
The siege has created medical and food shortages, exacerbating dire humanitarian needs created by regular government bombardment of the area.
More than 210,000 people have been killed in Syria since the beginning of the country's conflict in March 2011.