Air strikes on a market killed at least 29 civilians, including children, in a town in northern Syria on Monday 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 rebel-held 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.
A photographer contributing to AFP saw massive destruction at the scene, with rubble from damaged buildings covering the street and panicked civilians carrying away the injured.
Three men helped one of those hit in the attack, his face drenched in blood and his features almost completely obscured.
Nearby, the body of a man in a blue shirt and dark trousers lay where he had died.
Civil defence workers rushed alongside civilians to evacuate the injured, with one man in a thick beanie hat carrying a wailing child in a pink sweater away from the scene.
Elsewhere, the bodies of at least three children were laid out on the ground, partly covered by thick bolts of fabric.
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.