The British-based Syrian Observatory for Human Rights says the killings occurred in the town of Kfar Owaid in the northwestern province of Idlib on Tuesday. It says 111 people died. The Local Coordination Committees, another activist group, says more than 100 people were killed in the town.
The two groups had earlier reported that regime troops attacked the town with heavy machine gun fire and shelling, killing dozens.
The U.N. says more than 5,000 people have been killed in the crackdown.
Wednesday's reports come ahead of the arrival of an Arab League advance team to prepare for an observer mission.