Western governments prepared to send their top diplomats to lobby for a UN resolution condemning the Syrian regime's deadly crackdown as Russia said that it opposes the proposed text.
US Secretary of State Hillary Clinton said the UN Security Council "must act" to end President Bashar al-Assad's "violent and brutal attacks" against demonstrators after adopting not a single resolution since the protests erupted in March last year.
Clinton said she would travel to the United Nations on Tuesday to "send a clear message of support to the Syrian people -- we stand with you."
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The Syrian opposition flatly rebuffed a Russian call for talks with Assad's regime as violence across Syria killed 53 people, 35 of them civilians, activists said.
On Sunday, 80 people were reportedly killed, equally divided between military and civilian deaths, in the most intense clashes since the 10-month-old uprising began, the Syrian Observatory for Human Rights said.
Dramatic amateur footage claims to show a government tank being blown up, below.
The latest spike in violence, on top of what the United Nations said at the start of January already added up to 5,400 killings, pushed the Arab League to suspend a much criticised observer mission to Syria on Saturday.
French Foreign Minister Alain Juppe too is to head to New York on Tuesday to press the Security Council into taking action over the Assad regime's "crimes against humanity," his ministry said.
Foreign ministry spokesman Bernard Valero said a ministerial meeting at the UN on Tuesday would allow the Security Council to listen to the Arab League's report on the situation in Syria.
The Foreign Office in London said that Foreign Secretary William Hague would also go to the Security Council, although Juppe admitted that "conditions aren't yet right to get a resolution passed, because Russia is still reluctant."
Russian Deputy Foreign Minister Gennady Gatilov said the latest draft tabled by Morocco on Friday was little different to one Moscow and Beijing vetoed last October.
"The current Western draft has not gone too far from the October version, and, certainly, cannot be supported by us," Gatilov told Interfax news agency in an interview.
"The draft has statements in it calling on the member states to stop arms deliveries to Syria," he said.
Moscow, which has close ties with its Soviet-era ally, said earlier that Damascus had agreed to its offer to host talks with opposition representatives.
But the head of the Syrian National Council (SNC) said that the opposition rejects all talks with the Damascus regime until Assad steps down.
"The resignation of Assad is the condition for any negotiation on the transition to a democratic government in Syria," Burhan Ghalioun told AFP.
The position was echoed by the second largest opposition grouping, the Syrian National Coordination Committee for Democratic Change.
"Any negotiation or meeting is inconceivable in the shadow of the growing violence and killings, and the persistent arrests," its leader Hassan Abdel Azim told AFP.
Regime forces, who were reported to have executed a founder of the rebel army, appeared determined to wrest back control of Damascus suburbs which have intermittently fallen into the hands of the rebels.
Near the capital, 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, the Observatory said.
Activists at the scene said rebel troops pulled out of Rankus as the army moved in, while, in the eastern suburbs, snipers were "shooting at everything that moves" in Irbin and Hammuriyeh.
The SNC 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 received in Nicosia.
Elsewhere in Syria, the Observatory said at least 20 civilians were killed when security forces stormed the flashpoint central city of Homs, among them a doctor and a young girl.
Five civilians were killed in the Damascus suburbs and one in Idlib province in the northwest.
An ambush by deserters killed six loyalist troops in Daraa province, south of the capital. Two more were killed in Idlib.
A total of 10 rebel soldiers were also killed -- four in Daraa, two in Homs, two in Idlib and two in Rankus, the Britain-based watchdog added.
Free Syrian Army Colonel Hussein Harmush, a founder of the rebel group formed from army defectors, was executed last week, said the Syrian League for Human Rights, in a report which could not be independently confirmed.
In June last year, Harmush became the first Syrian officer to publicly declare his opposition to the regime's deadly crackdown on protesters.
Harmush left Syria to seek asylum in Turkey, where he established the Brigade of Free Officers, a group of dozens of deserters later absorbed into the Free Syrian Army headed by Riyadh al-Asaad.
Months later, his "confessions" were aired on Syrian state television after his return home in unclear circumstances.
