At least 43 civilians, including 11 children, were killed in bombardment of several rebel-held areas across Syria on Thursday, the Syrian Observatory for Human Rights monitor said.
The group said at least 13 people, including three children, were killed in government air strikes and shelling on the Eastern Ghouta area outside the capital Damascus.
Among the areas targeted was Douma, where the central market was hit, an AFP photographer said.
Government bombardment also hit two neighbourhoods of the rebel-held east of Aleppo city, where 15 people were killed, among them six children, the Observatory said.
Opposition-held neighbourhoods of Aleppo have been effectively under siege for the past two weeks, after government forces advanced to within firing range of the only remaining supply route into the east of the city.
Since then, government forces have seized part of the road, completely severing the east of the city from the outside world.
The Observatory also reported 15 civilians dead in air strikes in the town of Tal Manas in the northwestern province of Idlib.
But it was unable to confirm if the strikes were carried out by the Syrian government or its Russian ally.
The monitor -- which relies on a network of sources inside Syria for its information -- says it determines what planes carried out raids according to their type, location, flight patterns and the munitions involved.
A key ally of the Syrian government, Russia began carrying out air strikes in the country in late September.
More than 280,000 people have been killed in Syria, and more than half the country displaced, since the conflict began with anti-government protests in March 2011.