Cairo: At least 53 people were killed in air raids on a market in a northern Syrian town that is part of a so-called de-escalation zone, a monitoring group says.

The market in rebel-held Attareb, to the west of Aleppo, was hit by at least three raids on Monday, the Britain-based Syrian Observatory for Human Rights said, adding that it was not clear if they were carried out by by Syrian or allied Russian warplanes.

People inspecting damage from airstrikes on Atareb, in the opposition-held countryside outside Aleppo on Monday. Credit:Thiqa/AP

Local activists posted pictures online of massive damage and dead men, women and children. They also posted videos of panic-stricken civilians carrying the badly injured. Five children were among the dead, according to the Observatory.

"De-escalation zones" were set up earlier this year under a deal signed by Syrian government allies Russia and Iran, and Turkey, one of the Syrian opposition's main backers.