BEIRUT — Anti-regime activists in Syria said Friday that government gunners rained shells on a poor, farming village before armed thugs moved in, leaving scores of people dead in what rebels claim could be one of the worst single days of bloodshed in the uprising against Bashar Assad's regime.

The accounts — some of which claim more than 200 people were killed in the violence Thursday — could not be independently confirmed, but would mark the latest in a string of brutal offensives by Syrian forces attempting to crush the rebellion.

The head of the U.N. monitoring mission in singled out government forces forces for blame, saying they attacked from the air and ground in "continuous violence."