David Cameron today warned Russia and China not to block international moves to condemn the violent suppression of anti-government protests in Syria.
The Prime Minister confirmed that Britain and France would be formally tabling a draft resolution at the United Nations Security Council in New York demanding an end to the repression.
However they face potential opposition from Moscow and China who have indicated they are prepared to use their vetoes as permanent members of the 15-strong Security Council to block the move.
In the Commons at Prime Minister's Questions, Mr Cameron described the violence meted out to the demonstrators in Syria as "completely unacceptable" and said that the international community should come together to condemn it.
"If anyone votes against that resolution or tries to veto it, that should be on their conscience," he said.
Diplomats at the UN have yet to decide whether or when to put the resolution to a vote. There are hopes that Moscow and Beijing may still have to change tack, finding it difficult to wield their vetoes in the face of the worsening situation.
Mr Cameron said that there were "credible reports" that as many as 1,000 people had been killed and 10,000 detained since the regime's crackdown began.
The decision now to table a draft resolution - which has been circulating for more than two weeks - reflects a growing impatience in Western capitals with Syrian President Bashar Assad.
In a notable hardening of the diplomatic language, Foreign Secretary William Hague yesterday warned that Mr Assad was losing legitimacy and should "reform or step aside".
However there are also concerns that if he is forced out and the regime collapsed, the country could rapidly descend into sectarian violence with potentially serious implications for the entire region.
"We are worried about increasing sectarian violence. Iraq and Lebanon are clear reminders of the risks. The implications for the stability of the region are also very worrying," said one senior British official.
"On the other hand could I still see a future which had Assad as part of a reformed regime with a more plural political process? Potentially, but every day it is getting increasingly difficult to see that."