* Assad's man in Baghdad jumps ship and backs rebellion
* Tanks and mortars fire in south Damascus raid on rebels
* Opposition buoyed by defection
By Mariam Karouny and Erika Solomon
BEIRUT, July 12 (Reuters) - The first ambassador to abandon Syrian President Bashar al-Assad has called on the army to "turn your guns on the criminals" of the government, as troops swarmed into a suburb of the capital on Thursday to flush out rebels.
Nawaf al-Fares, who has close ties to the security services, was Syria's ambassador to its neighbour 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, Fares's defection gave the anti-Assad uprising one of its biggest boosts in 16 months of bloodshed.
Tlas, the son of a veteran former Syrian defence minister, has made no public comment since fleeing to Paris. But Fares posted a video statement on Facebook on Wednesday that repeatedly said government forces had been killing civilians.
"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 and calling for Assad to go.
"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.
The defection was seized on by Assad's opponents and by Western and Sunni Arab powers who insist that Assad must leave power in any political settlement for Syria.
"RELIEVED OF HIS DUTIES"
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."
While the insurgents cannot match the 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 rebels out of Kfar Souseh, a southern suburb.
The al-Lawan and Basateen districts of Kfar Souseh are a semi-residential area of olive and fruit groves lying astride an interchange on the capital's Hafez al-Assad southern bypass.
Activists said tanks were firing from the big Hadi Mosque to the east of the fields, and from the 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. And now I just heard another one hit. We can see fire and smoke coming from one of the fields nearby," 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 had killed a number of rebels who had been transporting arms and ammunition in two boats on Lake Qotaina, near Homs.
Assad's opponents say just under 13,000 armed and unarmed opponents of Assad, and around 4,300 members of security forces loyal to Damascus, have been killed since the uprising began 16 months ago.
With events on the ground outrunning diplomacy, Britain circulated a draft resolution, backed by the United States, France and Germany, at the United Nations on Wednesday to 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 authorise actions ranging from diplomatic and economic sanctions to military intervention.
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 draft in particular threatens the Syrian government with sanctions if it does not stop using heavy weapons and withdraw its troops from towns and cities within 10 days.
But Russia, Assad's chief backer on the U.N. Security Council, remained firmly in the Syrian leader's camp, having submitted its own draft resolution on Tuesday that made no mention of sanctions.
Russia's Deputy U.N. Ambassador Alexander Pankin told reporters after Annan briefed the council in New York on Wednesday that Moscow believed sanctions were a "last resort".
Russia and China, both veto-wielding permanent council members, 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.
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 as 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.
"Although Ambassador Fares is not a member of Assad's inner circle, he's a respected Sunni figure, and such a courageous act could help sway other Sunni elites to follow in his footsteps," said one U.S. official, speaking on condition of anonymity.
Western supporters of the rebel cause have been active in encouraging defections, which they see as one of the few tools available to them at the moment to undermine Assad. (Additional reporting Michelle Nichols at the United Nations and John Irish in Paris; Writing by Douglas Hamilton; Editing by Kevin Liffey)