Nations on the UN Security Council braced for a showdown over Syria, with US Secretary of State Hillary Clinton leading a Western charge to press Russia to back action to stop the violence.
Amid dozens of new deaths in Syria and opposition warnings of a potential massacre, Clinton, the head of the Arab League and the foreign ministers of Britain and France headed to New York to push forward a UN resolution Tuesday.
But Russia has vowed to use its veto power to block a resolution introduced by Morocco under which Syrian President Bashar al-Assad would accept a ceasefire and hand over power to a deputy ahead of talks on a settlement.
"The United States condemns in the strongest possible terms the escalation of the Syrian regime's violent and brutal attacks on its own people," Clinton said in a statement Monday announcing her trip to the United Nations.
"The Security Council must act and make clear to the Syrian regime that the world community views its actions as a threat to peace and security. The violence must end, so that a new period of democratic transition can begin," she said.
Clinton said that the Security Council session aimed to send a clear message from the international community to the Syrian people: "We stand with you."
European Union leaders at a Brussels summit unanimously voiced outrage over the bloodshed in Syria. EU President Herman Van Rompuy called on the Security Council to "take long overdue steps to bring an end to the repression."
British Prime Minister David Cameron, citing reports that more than 400 children have been killed in the crackdown, said: "It's frankly an appalling situation."
"It's time for all the members of the UN Security Council to live up to their responsibilities instead of shielding those with blood on their hands," Cameron said.
Russia and China, which have accused Western nations of misusing a UN mandate to depose Libyan strongman Moamer Kadhafi, in October vetoed an earlier Western-backed draft resolution on Syria.
Russian Deputy Foreign Minister Gennady Gatilov said that the latest draft resolution was little different. Russia has longstanding ties to Syria and is the main supplier of weapons to Assad's regime.
"The draft has statements in it calling on the member states to stop arms deliveries to Syria," Gatilov told Interfax news agency in an interview.
"But there is no clear line between arms contraband that some countries engage in to support extremist forces in Syria, and the legal military-technical ties with this country," he said.
Russia has instead called for Assad's regime and the opposition to hold "informal contacts" in Moscow without any preconditions.
Asked about Russia's call for talks, White House spokesman Jay Carney said the United States supported a political solution but was "intensely discussing" with Russia the "real deterioration on the ground" in Syria.
"The regime has lost control of the country and will eventually fall," Carney said.
Human rights groups say that more than 5,400 people have died in Syria as Assad tries to crush the latest in a wave of Arab uprisings that last year overthrew authoritarian leaders in Egypt, Libya and Tunisia.
Activists said that another 53 people were killed Monday -- 35 of them civilians -- a day after 80 people were reported to have died in some of the most intense clashes since anti-Assad protests erupted 10 months ago.
Regime forces appeared determined to wrest back control of Damascus suburbs which have intermittently fallen into the hands of the rebels and were reported to have executed a founder of the rebel army.
Troops penetrated Rankus, 40 kilometres (25 miles) north of the capital, after having shelled the town which the army had encircled for the past six days, rights groups said.
The opposition Syrian National Council warned of the potential for a massacre in Rankus after hundreds of young men were rounded up by security forces.
"They have imposed a siege on Rankus, preventing food and medical aid from entering" the town of 25,000 inhabitants, it said in a statement.
Before heading to New York, Arab League chief Nabil al-Arabi urged Russia and China to change their position, saying that deteriorating conditions had led Arab monitors to suspend their mission to Syria.
In Paris, French foreign ministry spokesman Bernard Valero urged action against "the Syrian regime's savage repression."
French Foreign Minister Alain Juppe will seek to "persuade the Security Council to assume its responsibilities faced with the Syrian regime's worsening crimes against humanity," Valero told journalists.
A French diplomat, speaking on condition of anonymity, said that opinions have "evolved" within the council and at least 10 of the 15 members could vote in favor of the draft resolution.