Foreign Secretary William Hague urged the "discredited" Syrian regime to end its violent repression as the United Nations Security Council adopted a statement condemning attacks on civilians and widespread human rights abuses.
Prompted by an intensification of the three-month-old bloody crackdown against anti-government protests, the international body agreed the wording - with only Syria's neighbour Lebanon dissociating itself from the text.
Mr Hague said: "I welcome the UN Security Council Presidential Statement on Syria.
"The support for this statement throughout the security council demonstrates the rising international concern at the unacceptable behaviour of the regime and shows that President Assad is increasingly isolated. It comes on top of a fourth round of EU sanctions put in place earlier this week.
"As I have made clear, it is vital that the violence and repression by the Syrian regime stops. The Syrian people are calling for peaceful change. I call on President Assad's regime to end its violence and to allow genuine political reform.
"Until it does, the regime will be discredited amongst its own people and facing increased pressure internationally."
Troops and tanks were deployed to the besieged city of Hama at the weekend, with casualties reported to be mounting rapidly - increasing pressure on the 15 members of the Security Council to issue a condemnation of the regime's actions.
Russia, China, India, Brazil and South Africa had been resisting the move.
The presidential statement expresses "grave concern at the deteriorating situation in Syria, and expresses profound regret at the death of many hundreds of people" and "condemns widespread violations of human rights and the use of force against civilians by the Syrian authorities".
It also expresses regret over "the lack of progress" by the government in implementing promised reforms.
Although it does not have the force of a UN Security Council Resolution, such a statement does form part of the international body's formal record.
Speaking on behalf of France, Germany and Portugal as well as the UK, Britain's UN ambassador Sir Mark Lyall Grant said the statement "delivers a clear, unambiguous and united message to the Syrian regime: barbarous acts must cease in Syria".
"The Syrian people have a right to liberty, democracy and justice," he said. "Damascus must respond quickly and unequivocally to these legitimate aspirations."
Human rights groups say at least 140 people have been killed since Sunday, mainly in Hama, taking the estimated overall death toll to around 1,500.Reuse content