The US has called on countries to decide where they stand on what it calls the Syrian regime's brutality.
Activists say 95 people were killed across Syria on Monday in cities including Damascus and Homs.
The White House said President Bashar al-Assad had lost control of Syria, adding "he will go".
Russia has said it will block a UN resolution calling for Mr Assad to hand power to a deputy who would then form a government of national unity.
Moscow said the text - proposed by the Arab League and backed by the US, the UK and France - was "not balanced" and would "leave open the possibility of intervention" in Syria's affairs.
White House spokesman Jay Carney: "Assad's fall is inevitable... The regime has lost control of the country"
The Local Co-ordination Committees, a network of anti-government groups, said on its Facebook page Monday's death toll was 95, including 72 in the central city of Homs. In Deraa, in the south, 15 people were killed, while six deaths were reported in the Damascus suburbs.
Their claims cannot be independently verified, as the the BBC and other international media are severely restricted inside Syria.
However, heavy machine-gun fire was reported in the restive Bab Amr district of Homs, while activists said at least 225 tank shells were fired at the eastern suburbs of Damascus.
Earlier, reports said the Syrian army had regained control of some Damascus suburbs recently held by rebel force... >>>
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