Pressure mounted on Syrian strongman Bashar al-Assad on Wednesday as Western powers sought a UN resolution that would give him 10 days to silence his heavy guns or face tough sanctions.
At the United Nations, Britain, France, Germany and the United States submitted a draft text that would impose tough measures on Damascus if Assad fails to implement UN-Arab League envoy Kofi Annan's plan.
If Security Council members, including a reluctant Russia, approve it, the resolution would allow for non-military sanctions under Chapter VII of the UN charter if Syrian government forces keep up their offensive on cities.
The resolution condemns "the Syrian authorities' increasing use of heavy weapons, including indiscriminate shelling from tanks and helicopters".
Negotiations on the Western draft and a rival Russian resolution, which does not mention sanctions, are to start on Thursday in New York. A vote must be held before July 20, when the mandate of the UN observer mission in Syria ends.
The draft calls for an "immediate" end to violence by government and opposition forces and demands government troops return to barracks in line with the Annan plan and UN resolutions passed in April.
If Assad has not "fully complied" within 10 days of the vote, the council "shall impose immediately measures under Article 41 of the UN Charter." Article 41 allows for economic and diplomatic sanctions but not military measures.
The resolution would renew the mandate of the UN Supervision Mission in Syria for 45 days, and calls on the mission to take on more political duties, moving away from monitoring a non-existent ceasefire.
The contingent of nearly 300 unarmed observers should be cut to "the minimum military observer capacity", the resolution says. According to diplomats, the UN leadership wants the observer numbers cut to 150.
Russia opposes the use of Chapter VII but its deputy UN ambassador, Igor Pankin, did not threaten a veto, insisting that negotiations have not even started over the rival texts.
"It is not a time for games, who vetoes first," Pankin said.
"It is a time for deciding on the future of Syria with Syrian plans and people and letting them engage. So I don't think we should be asking questions whether we veto it or not."
Earlier, Annan said the motion should include "clear consequences" for the regime if it fails to act and reported that even Syria's staunch ally Iran and nervous neighbor Iraq now "support the idea of a political transition."
The latest moves to end the 16-month-old conflict came as the regime continued to crumble from within, with Assad's ambassador to Baghdad joining a small but growing list of officials that have defected to the opposition.
Syria has been gripped by a vicious civil conflict since March last year, when the regime attempted to brutally suppress a pro-democracy revolt and triggered a broader uprising by armed insurgent groups.
Western powers and Syria's Arab and Turkish neighbors have called for Assad to stand down and allow a negotiated political settlement, but Damascus' ally Russia and thus far Iran have stood by him.
The regime and the opposition publicly accept Annan's plan, which has seen unarmed observers deployed to monitor a theoretical ceasefire, but fighting has raged on and rights monitors estimate that 17,000 Syrians have died.
"The Council is now discussing what the next steps should be and what action they can take," Annan told journalists, after privately briefing the 15-member UN Security Council by videophone from Geneva.
"We should hear something in the next few days."
Annan was just back from a tour of the region in which he met Assad and Iranian and Iraqi leaders. He said he and Assad had discussed the nomination of an interlocutor to negotiate with the opposition on behalf of the regime.
"In all frankness, yes we discussed it. He did offer a name. I indicated that I wanted to know a bit about the individual," Annan said, without giving any further details.
Russia's veto of two previous resolutions angered Syrian opposition leaders, who visited Moscow this week to try to persuade the Kremlin to drop its support for Assad's regime, Moscow's key Middle East ally.
"We reject the Russian policy -- however it is presented -- as this policy of supporting the regime is allowing the violence to continue," Abdel Basset Sayda, head of the exiled Syrian National Council, said after the talks.
"As a result, the killings and shootings continue and the Syrian regime is using these weapons that Russia gave to Syria against its own people."
Violence across Syria killed 52 people on Wednesday, 23 of them civilians, 18 soldiers and 11 rebels, according to a Britain-based rights watchdog, which added that 82 people had died the previous day.
It also reported an attack on a bus transporting troops in the northwestern province of Idlib that left as many as 11 dead.