Syria’s prime minister has defected to the opposition seeking to overthrow what fleeing premier Riyad Hijab called the “terrorist regime” of President Bashar al-Assad, marking one of the highest profile desertions from Damascus.

I have joined the ranks of the freedom and dignity revolution

Mr Hijab, who like much of the opposition comes from Syria’s Sunni Muslim majority, is not part of Mr Assad’s inner circle, but as the most senior serving civilian official to defect, his departure dealt a heavy symbolic blow to an establishment rooted in the president’s minority Alawite sect.

His departure is unlikely to have repercussions for Mr Assad’s grip on power. That is rooted in the army and a security apparatus dominated by Alawites, which was rocked by a bomb last month that killed four senior officials, including his brother-in-law.

Syrian state television said Mr Hijab had been fired, but an official source in the Jordanian capital Amman said he had been dismissed only after he fled across the border with his family.

“I announce today my defection from the killing and terrorist regime and I announce that I have joined the ranks of the freedom and dignity revolution,” Mr Hijab said in a statement read in his name by a spokesman and broadcast by Al Jazeera.

“I announce that I am from today a soldier in this blessed revolution.”

Khaled al Hbous, a senior figure in the rebel Free Syrian Army for the area around the capital, said that his fighters had helped Mr Hijab flee the country: “Between 5.30 and 7.30 this morning we did it,” he told Reuters by telephone.

“We secured his entry to Jordan and the Jordanian army took him from us.” He gave no details – Damascus lies 100 km from the border – but said more high-level defections would follow. The opposition Syrian National Council said a further two ministers and three army generals had defected with Hijab.

That assertion could not immediately be verified.

Syrian state television reported Mr Hijab’s dismissal as government forces appeared to prepare a ground assault to clear battered rebels from Aleppo, the country’s biggest city.

There was also violence near the capital, where rebels said government shelling had killed three Iranians they were holding. They threatened to kill other captives if the army did not halt its attack.

Mr Hijab was a top official of the ruling Baath party but, like all other senior defectors so far from the government and armed forces, he was also a Sunni and had no real authority over a state ruled by the Assads for the past four decades.

“Hijab is in Jordan with his family,” said the Jordanian official source, who did not want to be further identified, adding he defected to Jordan before his sacking.

Mr Assad appointed Mr Hijab, formerly agriculture minister, as prime minister only in June following a parliamentary election which authorities said was a step towards political reform but which opponents dismissed as a sham.

Mr Hijab’s home province of Deir al-Zor has been under heavy Syrian army shelling for several weeks as Assad’s forces try to dislodge rebels from large areas of countryside there.

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