Syria's ambassador to Iraq has defected to the opposition and urged other senior Syrian politicians and members of the military to do the same.
Nawaf Fares is the first senior Syrian diplomat to abandon the government of President Bashar al-Assad.
Syria's foreign affairs ministry has responded by formally dismissing him from his post, Sana news agency says.
Mr Fares's defection comes just a week after a Syrian general from a powerful family close to President Assad also defected.
He confirmed his decision in a statement broadcast on Facebook and al-Jazeera TV.
With Syrian revolutionary flags behind him, he read out the statement saying he was resigning both as Syria's ambassador to Iraq and as a member of the ruling Baath Party.
Head of Sunni Uqaydat tribe, straddling Syria's eastern border with Iraq
Served as top Baath Party official in Deir al-Zour province
Appointed Baghdad ambassador 16 Sept 2008
First Syrian envoy to Iraq for nearly three decades
Resigns from Baath Party and as ambassador 11 July 2012
"I call on all party members to do the same because the regime has transformed it into a tool to oppress the people and their aspirations to freedom and dignity.
"I announce, from this moment on, that I am siding with the people's revolution in Syria, my natural place in these difficult circumstances which Syria is going through."
Syria's foreign ministry said he had made statements that contradicted the duties of his post and no longer had any relation to the Syrian embassy in Baghdad.
Mr Fares, significantly, is also chief of a Sunni tribe straddling Syria's eastern border with Iraq, our correspondent adds.
That area, around the city of Deir al-Zour, has become a hotbed of support for the rebels and has been heavily bombarded in recent weeks.
Syria has been convulsed by internal conflict since protests against President Assad began early last year. The protests turned into an armed rebellion and thousands of people have been killed.
Last week, senior army officer Brig Gen Manaf Tlas fled Syria via Turkey.
He was a commander of a unit of the elite Republican Guard and as a young man he attended military training with President Assad.
Gen Tlas had been under a form of home arrest since May 2011 because he opposed security measures imposed by the regime, sources said.