Nawaf Fares, the first Syrian ambassador to defect to the opposition, was widely seen as a regime hardliner and his decision to break ranks has triggered suspicion among activists.
Some dissidents say Fares has been likely groomed by the West to play a role in a transitional government while others have spoken about his "criminal" past.
Fares, who has served as governor in several Syrian provinces and has held senior security and Baath party posts, hails from the prominent Oqaydat Sunni tribe in eastern Syria, which also has members in Iraq, Jordan and Saudi Arabia.
A former policeman, Fares had close ties to the dreaded intelligence services before becoming governor and later Syria's first ambassador to Iraq following a 30-year rupture in ties between the two neighbours.
He announced his defection on Wednesday, as the regime battles a growing rebellion that has claimed, according to monitors, more than 17,000 lives since it erupted in mid-March 2011.
"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.
"I call on all free and worthy people in Syria, particularly in the military, to immediately rejoin the ranks of the revolution," said Fares, a grey-haired man who sports a bushy moustache and wears glasses.
"Turn your cannons and your tanks towards the criminals in the regime who are killing the people," he added.
On Thursday the Syrian foreign ministry said Fares has been "discharged" and "needs to be legally prosecuted and subjected to disciplinary action" due to his remarks which contradict his duty.
Fares, the first ambassador to break ranks with the regime, announced his defection only days after Manaf Tlass, a top general with close ties to President Bashar al-Assad, deserted.
Fares hails from the city of Al-Bukamal in the eastern province of Deir Ezzor, near the border with Iraq. He holds a degree in law and graduated from the Deir Ezzor police academy.
He began his career as head of political security in the coastal province of Latakia (1990-1994) before heading the ruling Baath party in Deir Ezzor until 1998 when he served as governor of Latakia for two years.
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For the next two years he was governor of the northeastern province of Idlib, where anti-regime sentiment is now strong, and from 2000 he served eight years as the governor of Quneitra, capital the Golan Heights most of which is annexed by Israel.
On September 16, 2008, Assad appointed Fares as Syria's first ambassador to Iraq in 30 years -- a clear show of trust in the new envoy.
His new mission was delicate and centred on healing ties between the two neighbours, particularly as Iraq was accusing Syria of allowing Islamist fighters to cross the border to carry suicide attacks in the country.
-- 'Power thirst and bloody hands' --
On Wednesday, Fares, who is now believed to have sought refuge in Qatar, a vocal critic of Assad's government, turned on the regime.
His change of heart however has failed to persuade opponents of the regime and activists.
"I know this man is a criminal," said Rami Abdel Rahman of the Syrian Observatory for Human Rights which has tallied the death toll from 16 months of violence at more than 17,000 people.
"It's quite similar to the Manaf Tlass story. If the ambassador defects, he does it because he is greedy for power because Western intelligence agencies are looking for figures who can fit into a transitional phase," Abdel Rahman said.
An activist in the central Syrian city of Hama, who identified himself as Abu Ghazi, shares this view. "People are very wary of the reasons he has defected," he said.
"This defection could be part of a scenario at a time when Russia is starting to slightly shift in its position, and while the international community and the regime are searching for ways to establish a transitional government," Abu Ghazi added.
"We want to live in a democracy, in a state of law and you can't build that with people who have so much blood on their hands and who have been complicit for so long with the regime."
Not so, say supporters of Fares on the website of his Oqaydat tribe.
"He excelled in all his public duties... He honoured his tribe and has become a symbol for Deir Ezzor thanks to his modesty and the love he has for people," wrote one supporter.