The death toll in the air strikes against a market in the Syrian rebel-held town of Atareb rose to 61 on Tuesday, said the Syrian Observatory for Human Rights, adding that the majority were civilians.
Head of the monitor Rami Abdul Rahman said that a number of people died from injuries they sustained during Monday’s strikes, bringing the toll to 61, including five children.
Three members of the local police were among the victims.
Three strikes hit the northern town of Atareb despite a "de-escalation zone" in place there.
The Britain-based monitor said it was not clear whether the bombing raids had been carried out by Syrian regime warplanes, or those of its ally Russia.
The Observatory expected the toll to rise as more victims are retrieved from under the rubble.
A photographer contributing to AFP saw massive destruction at the scene on Monday, with rubble from damaged buildings covering the street and panicked civilians carrying away the wounded.
Atareb is in the west of Aleppo province, in an area that is part of a "de-escalation zone" agreed under a deal reached earlier this year between Syria's allies Russia and Iran, and rebel-backer Turkey.
The zone mostly covers neighboring Idlib province.
Despite the regime’s recapture of Aleppo city late last year, rebel groups maintain a presence in the west of the province.