US Secretary of State Hillary Clinton said there was "indisputable evidence that the regime deliberately murdered innocent civilians," and urged the UN Security Council to take action.

"History will judge this Council. Its members must ask themselves whether continuing to allow the Assad regime to commit unspeakable violence against its own people is the legacy they want to leave," Clinton said.

Norwegian Maj. Gen. Robert Mood, the head of the mission, told reporters in Damascus that a group of his monitors had managed to move to within about 5 kilometers of Tremseh on Thursday as the killings took place. He said they had confirmed the use of attack helicopters and heavy weapons.

UN leader Ban Ki-moon on Friday said that a failure by the council to respond would be "a license for further massacres."

The UN-Arab League peace envoy has asked for a strong message in light of reports of a massacre of dozens of people in Syria this week.

In a letter to the Security Council, Kofi Annan said the accounts of killings were yet another "reminder that the Council's resolutions continue to be flouted."

He also said the events that unfolded in the central Syrian village made it more urgent than ever that the Security Council demand that its resolutions be implemented by the parties to the conflict "and sends a message that there will be consequences for noncompliance."

In the letter, Annan referred to the findings of UN military observers in Syria.

Dozens killed

Opposition activists say at least 200 people were killed in the village in shelling and a subsequent raid by pro-government Alawite militiamen. Some reports put the death toll significantly lower.

Severe restrictions placed on journalists have made it virtually impossible to independently confirm this and other casualty figures being reported in the country.

For the past several weeks, UN monitors have largely remained in Damascus because of the continuing violence. Government forces have also prevented the monitors from visiting the sites of past reported massacres. 

The Syrian government has confirmed that its forces were involved in an operation in Tremseh on Thursday, but it has denied that any civilians were targeted.

"Army units carried out a special operation targeting armed terrorist groups and their leadership hide-outs," a Syrian military spokesperson said. "The terrorists were dealt with, while there were no civilian victims."

Annan's next stop: Moscow

Annan, whose peace plan appears to have been virtually ignored by all of the parties to the conflict, is expected to travel to Moscow on Monday for talks with senior Russian officials, including President Vladimir Putin and Foreign Minister Sergei Lavrov.

Russia, which has repeatedly used its position as a permanent member of the UN Security Council to shield the Assad regime from international sanctions, condemned Thursday's violence in Tremseh but did not apportion blame.

A spokesman for Chancellor Angela Merkel told reporters in Berlin on Friday  that Germany has demanded that Syria grant immediate access to UN observers so that they could launch a full investigation into the reported massacre.

Germany has a seat on the Security Council as a nonpermanent member.

pfd, rc/mr (AP, Reuters, AFP)