Syrian pro-government forces have killed 78 people in a single village in Hama province, many of them women and children, amid fears militia are turning to sectarian violence.
Opponents of the government said that government-backed militia stabbed and shot their victims in the village of Al-Kubeir, also known as Mazraat al-Qubeir , the BBC reports.
Damascus denied a massacre, saying "terrorists" had killed nine people.
Neither account could be confirmed, but activists said 140 had been killed nationwide on Wednesday - one of the bloodiest days of the uprising.
It comes less than two weeks after 108 people were killed in a massacre in Houla, and the BBC reported it seems some militia groups were operating independently, targeting victims on sectarian lines.
Analysts say the continuing unrest suggests diplomatic efforts to resolve the crisis are having little impact on the ground, even though UN-Arab League envoy Kofi Annan is expected to urge the UN Security Council to create a new contact group to help end the violence.
So far, Kofi Annan's plan has unsuccessfully called for a ceasefire, followed by a dialogue between the government and the opposition that would lead to a political transition.
Instead there's been an upsurge in violence, with the regime accused of carrying out massacres, and the rebels stepping up deadly attacks on soldiers.
UK Prime Minister David Cameron condemned the "brutal and sickening" killing of civilians and called for concerted international action.
Activist groups said much of the killing was done by accompanying groups of pro-government militiamen known as shabiha, who had come from nearby pro-government villages.
The activists said these militiamen shot at close range and stabbed many people, and that some of the bodies were later burnt in houses that were set on fire.
"They executed [nearly] every person in the village. Very few numbers could flee. The majority were slaughtered with knives and in a horrible and ugly way," one activist in Hama told the BBC.
"The small number of villagers who fled were the only people remaining who could tell the world about this horrible massacre."
One surviving resident told the BBC that when the army and militia left the village, he had discovered about 40 bodies - mostly women and children who had been stabbed to death.
Among the victims were four members of his family, the villager said. He added that he saw the burned corpse of a three-month-old baby.
The Local Co-ordination Committees, an activist network, said 78 people had died in Mazraat al-Qubeir, including 35 members of one family.