The first ambassador to abandon Syrian President Bashar al-Assad called on the army to "turn your guns on the criminals" of the government, as troops backed by tanks swarmed into a suburb of Damascus on Thursday to flush out rebels.
Nawaf al-Fares, who has close ties to the security services, was Syria's ambassador to its neighbor Iraq, one of its few friends in the region.
Coming just days after the desertion of Manaf Tlas, a brigadier general in the elite Republican Guard who grew up with the president, his defection gave the anti-Assad uprising one of its biggest boosts in 16 months of bloodshed.
But Syria's strongest ally, Russia, stuck by Assad on Thursday with a clear warning to his Western and Arab enemies that it would not even consider calls for a tough new resolution by the U.N. Security Council in New York.
Britain circulated a draft on Wednesday, backed by the United States, France and Germany, that would make compliance with a transition plan drafted by international envoy Kofi Annan enforceable under Chapter 7 of the U.N. Charter.
This would allow the council to authorize actions ranging from diplomatic and economic sanctions to military intervention.
But as council members began negotiations on a resolution to renew the U.N. Syria monitoring mission, Russia's Deputy U.N. Ambassador Alexander Pankin made clear Moscow would use its veto if it had to.
"We are definitely against Chapter 7," he said. "Anything can be negotiated, but we do not negotiate this, this is a red line."
Annan himself asked the 15-member council to agree on "clear consequences" if the Syrian government or opposition failed to comply with his plan, which has produced neither a ceasefire nor political dialogue since it was agreed in April.
The British draft threatens the Syrian government with sanctions unless it stops using heavy weapons and withdraws its troops from towns and cities within 10 days.
"PEOPLE ARE TERRIFIED"
While the insurgents cannot match the Syrian army's firepower, they have managed to establish footholds in towns, cities and villages across Syria, often prompting Assad's forces to respond with helicopter gunships and artillery.
On Thursday, residents reported the first bombardment of the capital as security forces used mortars, then tanks and infantry to try to flush out rebels near Kfar Souseh, a southern suburb.
Activists said tanks had fired from the Hadi Mosque to the east and al-Mazzeh military airport immediately to the west.
"I woke up this morning and saw helicopters flying over the area. Then I started hearing the mortars. There were about six or seven of them in the past half hour," said anti-government activist Hazem al-Aqad.
"People are terrified, families are getting in their cars and rushing away as fast as they can."
The official news agency SANA said Syrian forces killed rebels shipping arms in two boats on Lake Qotaina, near Homs.
Assad's opponents say 13,000 armed and unarmed opponents of Assad, and 4,300 members of security forces loyal to Damascus, have been killed since the uprising began 16 months ago.
The activist Syrian Observatory for Human Rights said 42 people had been killed so far on Thursday, 30 of them civilians.
Tlas, socialite son of a veteran former defense minister, has made no public comment since fleeing, but France said on Thursday he was in contact with Syrian rebels.
"I know the opposition and this general have approached each other ... contact has been made," said Foreign Minister Laurent Fabius. But he said he could not confirm Tlas was in Paris.
Fares by contrast immediately went public, posting a video statement on Facebook on Wednesday that repeatedly said government forces had been killing civilians.
"DEFEND THE COUNTRY"
"I declare that I have joined, from this moment, the ranks of the revolution of the Syrian people," he said.
"I ask ... the members of the military to join the revolution and to defend the country and the citizens. Turn your guns on the criminals from this regime ...
"Every Syrian man has to join the revolution to remove this nightmare and this gang," he said, accusing the Assad family and its allies of corruption and "destroying society" for 40 years.
Iraqi Foreign Minister Hoshiyar Zebari said Fares was now in Qatar, one of the Gulf states overtly supporting the rebels.
"He is a man of strong military and security background," Zebari told reporters in Paris. "We were surprised by his defection because he was a loyal member of the regime."
Assad's crackdown on what began as a broad, peaceful pro-democracy movement helped turn it into an armed rebellion, but the insurgents know they must erode the loyalty and conviction of his establishment to loosen its hold on power.
In Damascus, a terse government statement said: "The Syrian Foreign Ministry declares that Nawaf al-Fares has been relieved of his duties and he no longer has any link to our embassy in Baghdad or the foreign ministry. They embassy in Iraq will continue carrying out its normal duties."
A White House spokesman said: "I think the Syrian government's response is you can't quit you're fired, which is another sign of the desperation ... enveloping the Assad regime."
Russia and China, both veto-wielding permanent members of the U.N. Security Council, have for months blocked attempts to increase the pressure on Assad, endorsing his argument that he is defending his country against armed groups bent on toppling him with the backing of the West and Sunni Arab Gulf monarchies.
"Obviously we are talking with the Russians and others about what will happen after Assad leaves, but for the moment it's true that they haven't come round to our way of thinking," French Foreign minister Laurent Fabius told reporters.
"The Russians are not blind, they can see that there are defections."
Most of Assad's political and military establishment are members of the minority Alawite sect, an offshoot of Shi'ite Islam. The revolt and the fighters behind it are mostly Sunni Muslims, as are Tlas and Fares.
Their defections may indicate a growing alienation among the Sunni business elite, which had been slow to embrace a revolt that began among poorer parts of the majority community.
(Additional reporting Michelle Nichols at the United Nations and John Irish in Paris; Writing by Douglas Hamilton; Editing by Andrew Roche)