Pressure mounted on Syrian strongman Bashar al-Assad on Thursday after a first senior diplomat, his ambassador to Baghdad, defected and Western powers drew up a 10-day sanctions ultimatum.
Syria's ambassador to Iraq, Nawaf Fares, announced he was joining a small but growing list of officials who have defected to the opposition, as the regime battles a near 16-month-old uprising.
"I announce my defection from my post as representative of the Arab Syrian Republic in Iraq and my withdrawal from the ranks of the (ruling) Baath party," Fares said in a message aired on Al-Jazeera satellite channel late on Wednesday.
"I call on all free and worthy people in Syria, particularly in the military, to immediately rejoin the ranks of the revolution," he said, adding: "Turn your cannons and your tanks towards the criminals in the regime who are killing the people.
He also called on fellow Baath members to reject the regime which he accused of using the party as "a tool to repress the people and their aspiration of freedom and dignity."
The disaffected diplomat submitted a letter to the Iraqi foreign ministry and will meet with Iraqi officials on Thursday, a diplomat said.
At the United Nations, Britain, France, Germany and the United States submitted a draft text that would give Assad 10 days to implement UN-Arab League envoy Kofi Annan's ceasefire plan or face tough new sanctions.
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 that President Assad's troops return to barracks in line with the Annan plan and UN resolutions passed in April.
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 reduced 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.
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."
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 more than 17,000 Syrians have died.
Turkey meanwhile said it has found no traces of explosives on the wreckage of a fighter jet it has claimed was downed by Syria, raising new questions about the incident that inflamed cross-border tensions.
"No traces of explosives or flammable products were found on the debris recovered from the sea," a statement from Turkey's general staff said late on Wednesday, adding that other material was still being examined.
For the first time, the army also declined to use the term "shot down by Syria" instead referring to "our plane that Syria claimed to have destroyed."
Turkey has previously maintained that the F-4 Phantom was shot down in international airspace over the eastern Mediterranean by Syrian fire on June 22, further souring relations between the one-time allies.
The two-man crew perished in the incident.
Violence across Syria killed at least 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.