Nawaf Fares, the first senior Syrian diplomat to abandon President Bashar al-Assad's government, has called on other officials to do the same.
In a video statement via Al Jazeera, Fares confirmed that he had resigned his position as Syria's ambassador to Iraq, quit the ruling Baath party and joined the opposition.
"I urge all honest members of this party to follow my path because the regime has turned it to an instrument to kill people and their aspiration to freedom," he is quoted as saying.
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According to Reuters, Fares also had a message for the Syrian army: "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."
Syria's Foreign Ministry responded by announcing that Fares was fired for making "statements that contradict the duties of his position of defending the country's stances and issues," state news agency SANA reported.
The former ambassador is now in Qatar, Reuters quoted Iraq's foreign minister, Hoshiyar Zebari, as saying.
The BBC noted that Fares comes from a Sunni area in the east of Syria, Deir al-Zour, which has been heavily bombarded by government forces in recent weeks.
According to the New York Times, he is one of a growing number of high-ranking Sunnis – including former brigadier-general Manaf Tlas, who deserted last week – to have abandoned Assad's government, which is dominated by the president's fellow minority Alawites.
That pattern could be a sign that Syria's crisis is taking on an increasingly sectarian nature, the Times said.