Opposition activists say Syrian government troops using tanks and helicopters have massacred more than 200 people in the central province of Hama.
London-based Syrian Observatory for Human Rights said the massacre occurred in the village of Tremseh on July 12.
Reports of violence are difficult to confirm in Syria, where authorities maintain strict limits on independent reporting and international access to the fighting zones.
A rebel leader, Abu Mohamad, said the attackers used helicopters, tanks, and multiple rocket-launchers.
The state-run SANA news agency said there had been clashes between the army and an armed "terrorist" group in the village but made no mention of a massacre and suggested around 50 people had been killed.
The head of the opposition Syrian National Council, Abdel Basset Sayda, expressed outrage at the alleged massacre and called for a tough UN resolution that allows for military intervention against the Damascus regime.
The Syrian Observatory for Human Rights says more than 17,000 people have been killed since the uprising erupted in mid-March 2011.
Meanwhile, the United States has warned Syrian officials that they will be held “accountable” if they fail to safeguard the conflict-torn nation’s stocks of chemical weapons.
The State Department statement came after a report in “The Wall Street Journal”
said U.S. officials were concerned that part of Syria’s chemical weapons arsenal was being moved out of storage facilities.