DAMASCUS: Syria's prime minister Riad Hijab joined the anti-regime revolt and fled abroad, in what Washington and the opposition hailed on Monday as a major blow to President Bashar al-Assad.
Government forces, meanwhile, were poised to launch an assault on rebels in Aleppo, Syria's commercial capital, as a monitoring group said at least 137 people were killed in violence across the country.
In the highest-ranking defection of the nearly 17-month uprising, Hijab, a leading Sunni Muslim in Assad's minority Alawite-dominated regime, announced he was joining the rebels after crossing into Jordan on Sunday night.
He accused his former master of carrying out "genocide" against his own people but said four decades of Assad family rule were collapsing.
"I announce my defection today from the regime of killing and terror, and I join the ranks of the revolt," Hijab said in statement read by his spokesman Mohammed al-Otri on Al-Jazeera news channel from Amman.
Otri said the defector was headed for Qatar.
Hijab's home province of Deir Ezzor in the northeast has been one of the key battlegrounds of the conflict and seen a mounting death toll from operations by the army.
The latest defection shows Assad has lost control of the country and that his people believe his days are numbered, a US official in Washington told AFP.
The surprise development was "just the latest indication that Assad has lost control of Syria and that the momentum is with the opposition forces and the Syrian people," National Security Council spokesman Tommy Vietor said.
The Syrian opposition in Jordan said Hijab and his family had slipped over the border during the night accompanied by two government ministers and three army officers.
"The Free Syrian Army helped all of them cross the border... Several other army officers defected and arrived in Jordan last night," said Syrian National Council member Khalid Zein al-Abedin. (AFP)