BEIRUT - At least 21 civilians, including five children, were killed on Monday in air strikes on Syria's northern Aleppo province, despite a "de-escalation zone" in place there, a monitor said.
The Britain-based Syrian Observatory for Human Rights said it was not immediately clear whether the strikes on the rebel-held town of Atareb had been carried out by Syrian warplanes, or those of Damascus's ally Russia.
The monitor said three strikes hit the town's market, adding that the overall toll was expected to rise because dozens of people had been wounded or were still missing after the attack.
Atareb is in the west of Aleppo province, in an area that is part of a "de-escalation zone" agreed under a deal earlier this year between Syria's allies Russia and Iran, and rebel backer Turkey.
The zone mostly covers neighbouring Idlib province, which is largely held by opposition forces and a jihadist group formerly affiliated with Al-Qaeda.
Despite the government's recapture of Aleppo city late last year, rebel groups maintain a presence in the west of the province.
More than 330,000 people have been killed in Syria since the conflict began in March 2011 with anti-government protests.