Foreign Secretary William Hague today welcomed the United Nations' demand that President Bashar Assad pull back troops amid continuing violence with opposition protesters in Syria.
Hague's statement came amid fresh allegations of violence against civilians by Assad's forces.
The regime has said it accepts a peace plan by the UN-Arab League envoy Kofi Annan, but so far there has been little evidence that it is prepared to end its brutal crackdown on the opposition.
Turkish officials said more than 2,350 Syrian refugees had fled across the border in 24 hours.
Hague said the UN Security Council had "made clear that we will not accept any more broken promises or allow Assad's brutal assault to continue".
He said: "Today the Security Council has unanimously demanded that the Syrian regime meet its commitment to pull back troops by 10 April and end the violence, further backing Kofi Annan and his six point plan.
"It has made clear that we will not accept any more broken promises or allow Assad's brutal assault to continue.
"The Syrian authorities must prove to the international community and more importantly the Syrian people that they are sincere about ending the killing. If they do not, the Security Council must act to increase the pressure on the regime."
Attending the international "Friends of the Syrian People" conference in Istanbul at the weekend, the Foreign Secretary earlier accused Assad of "stalling for time".
Above: video shot in Homs and uploaded on 5 April appears to show missiles slamming into the city streets.
Later, former Labour Prime Minister Tony Blair told ITV News, Britain should "keep all the options open" in relation to Syria.
Commenting on the situation in an interview due to be shown on ITV News at Ten, Mr Blair said: "Already thousands of people have died and many thousands more will die.
"So these are decisions, when you intervene, it's always important to recognise if you intervene there will be consequences some of which are unpredictable and adverse and if you don't the consequences actually are more predictable and probably very adverse also."
He added: "I think the government is doing all it can do at this point in time, but I think we should keep all the options open.
"In particular, what is very important is that we carry on sending a very strong message to Assad and the Syrian regime that this is not something where they can just roll over the people and then we are going to say 'ok, let's just forget about it'.
"No, we will be there and be active in support of the Syrian people who want freedom and want the chance to elect their government."
He said: "All these situations are different and they are all tough, so having been in this position, trying to take these decisions, I'm not going to second guess the guy who is taking them now."