Video uploaded on the Internet and said to be shot on Thursday (January 3) purports to show the aftermath of several air strikes, including one on the eastern outskirts of Damascus and one in the town of Douma.
Opposition activists also said warplanes struck a residential building in another rebel-held northern town, Hayyan, killing at least eight civilians.
Video footage shows men carrying dismembered bodies of children and dozens of people searching for victims in the rubble of the destroyed building, shouting "God is greatest ". The provenance of the video could not be independently confirmed.
In addition to their tenuous grip on the north, the rebels also hold a crescent of suburbs on the edge of Damascus, which have come under bombardment by government forces that control the center of the capital.
On Wednesday (January 2), according to opposition activists, dozens of people were incinerated in an inferno caused by an air strike on a petrol station in a Damascus suburb where residents were lining up for precious fuel.
The civil war in Syria has become the longest and bloodiest of the conflicts that rose out of uprisings across the Arab world in the past two years.
Another unverified social media video clip, said to be shot on Thursday, shows rebels firing machine guns and Syrian army positions in the southern town of Busra al Hariri.
More than 60,000 people have died in Syria's uprising and civil war, the United Nations said on Wednesday, dramatically raising the death toll in a struggle that shows no sign of ending.