The shelling hit the Nafasin market in the rebel-held town of al-Bab, said Rami Abdurrahman of the British-based Observatory for Human Rights, who obtains his information from a network inside Syria.
An Aleppo-based activist who goes by the name of Abu Raed corroborated the report, saying said the strike was likely to attack fighters who filter through the town into rebel-held areas of eastern Aleppo. Abu Raed does not use his real name for fear of government reprisals.
Footage of the attack showed men rushing down a street strewn with rubble, made cloudy by dust. One man with a bloodied head lies still in a car. Bodies were strewn on the ground, as men hurried the wounded into cars and shouted orders at each other. The video was consistent with reporting by The AP.
Assad's forces have retaken a series of rebel-held areas surrounding Aleppo in recent weeks, tightening the noose around the key city, where rebels seized many neighborhoods last year.