Syrian government forces have killed at least 78 people, including many women and children, in a "massacre" that took place in the central Hama province, the opposition Syrian National Council has claimed.
Mohammed Sermini, spokesman for the coalition said: "We have 100 deaths in the villages of Al-Kubeir and Maarzaf, among them 20 women and 20 children."
Some of those killed in the village of Mazraat al-Qabeer were stabbed to death, the activists said, and at least 12 bodies had been burned.
Pro-regime shabiha militia armed with guns and knives carried out the "new massacre" at a farm after shelling by regular troops, the Britain-based Syrian Observatory for Human Rights said.
Sky's foreign editor Tim Marshall said: "If there have been fatalities both sides will blame each other. But the timing is just ahead of Kofi Annan's briefing the UN security Council about whether his peace plan and UN monitors are actually having an effect or not.
"If this (the massacre) is true it is going to play directly into that debate."
Rami Abdul-Rahman, the head of the Britain-based Syrian Observatory, called on UN observers to visit the area immediately.
The killings came less than two weeks after a massacre in the Syrian town of Houla, in which some 108 people were killed, nearly half of them women and children.
UN investigators have blamed pro-government gunmen for at least some of the killings.
The Syrian regime has denied responsibility and blamed rebels for the attacks.
Despite international condemnation over the violence in Syria, Russia and China have blocked the use of any military intervention by the UN Security Council and issued a joint statement reiterating their opposition to any imposing of "regime change".
The French foreign minister Laurent Fabius dismissed a Russian proposal for a global conference on Syria that would include Iran together with other powers.
"Iran can in no case be involved in talks as it would firstly be contradictory with the aim of applying strong pressure on Syria and would also have an effect upon Tehran's nuclear programme, which is not desirable," he said.
Foreign Secretary William Hague echoed him, saying: "I think the inclusion of Iran in any such group would probably render it unworkable.
"This is a country that is supporting some of the unacceptable violence and supporting the Syrian regime in what it is doing to the Syrian people and that would cause a great difficulty."