Syrian troops have been accused of massacring an entire village with rockets, machine guns and tanks.
They surrounded the unarmed villagers in a valley and killed all those trapped inside - more than 100 people - in a barrage that lasted for hours, a witness and two activist groups said.
The attack on Tuesday pushed the death toll for two days of violence across Syria to more than 200, and was one of the deadliest single events of the entire nine-month uprising against President Bashar Assad.
The offensive targeted the village of Kfar Owaid, about 30 miles from the northern border with Turkey. It is part of the rugged mountainous region of Jabal al-Zawiyah, which has been the scene of clashes between troops and army defectors and intense anti-government protests for weeks.
"It was an organised massacre," said Rami Abdul-Rahman, head of the British-based activist group Syrian Observatory for Human Rights. "The troops surrounded people then killed them."
One villager who escaped said that scores of people had fled to the nearby Budnaya Valley, where they were completely surrounded by troops. The man, who identified himself only as Abu Rabih for fear of government reprisal, said troops also used bombs filled with nails to increase the number of casualties.
"What happened yesterday was a crime against humanity," he said. He said 110 people were killed in the attack.
Activists said all the victims were unarmed civilians and activists.
Assad agreed on Monday to allow foreign monitors under an Arab League plan aimed at stopping the bloodshed. But the huge toll from the crackdown on Monday and Tuesday has reinforced opposition suspicions that he is just playing for time to stall a new round of international condemnation and sanctions. The crackdown has already left him internationally isolated and under tremendous pressure from the Arab world as well as the west.
The Arab League plan calls for Syria to halt its crackdown, open talks with the opposition, withdraw military forces from city streets and allow in human rights workers and journalists Despite intensified violence, the League appeared to be going ahead with its plans to send the monitors.