BEIRUT: Syrian President Assad’s grip on power appeared to be slipping Monday after his own prime minister, Riad Hijab, defected to the opposition. The news sparked new fears of retribution in Aleppo, where rebel forces are already bracing for an all-out assault by the Syrian Army.

Hijab, who Assad appointed to the premiership just two months ago, buoyed the regime’s opponents, who claimed it was the clearest sign yet of deep divisions within the Baath party.

Hijab, the former agriculture minister appointed prime minister, announced he was joining the rebels after crossing into Jordan early Monday.

Hijab accused Assad of carrying out “genocide” against his own people and said that four generations of Assad rule were collapsing.

“I announce my defection today from the regime of killing and terror, and I join the ranks of the freedom and dignity revolution,” Hijab said in a statement read by his spokesman Mohammad al-Otri on Al-Jazeera television from Amman.

“From today I am a soldier in this blessed revolution.”

Head of the opposition Syrian National Council Abdul-Basset Sayda said “this defection shows that the regime is disintegrating. It is the beginning of the end.” The exiled Muslim Brotherhood issued a statement calling the defection “a courageous expression of great nationalism.”

The White House hailed the defection as proof Assad’s government was “crumbling from within.”

“Assad cannot restore his control over the country because the Syrian people will not allow it,” White House spokesman Jay Carney said.

Hijab, a Sunni Muslim from eastern Deir al-Zor, which has recently come under heavy government shelling, is not part of Assad’s inner circle.

But analysts and diplomats say his defection deals a heavy psychological blow to the regime already rattled by the killing of four members of his crisis cell, including Assad’s brother-in-law, Assef Shawkat, in a bomb attack on the capital on July 18.While his role as prime minister under Assad held little real power, Hijab – a Baath party stalwart – was considered an unwavering loyalist.

He was promoted from agricultural minister to prime minister in June and had served as the head of the Baath party in Deir al-Zor. He later served as governor of the strategic Quineitra province bordering Israel, and as the governor of Latakia.

“He is from an important tribe and it was assumed he had complete loyalty,” said one Beirut-based diplomat. “I don’t know about the impact of this [on Assad’s grip on power] unless of there are a series of defections that follow.

“But symbolically what this does for the party and for the psychology of the whole civil service ... this is a huge blow,” the diplomat said.

Damascus issued a hasty report via state media announcing Hijab had been dismissed from his post. It said Deputy Prime Minister Omar Ghalawanji had been appointed as caretaker premier. Later, information minister Omran al-Zohbi said “the flight of some personalities” at any level would have no effect on the Syrian state, without referring to Hijab explicitly.

Rime Allaf, associate fellow at London’s Chatham House, said the defection was important in that “it proves the regime doesn’t know who it can count on anymore.”

She said it forced the regime to drop a pretense of control. “The regime has been trying for the last year and a half to tell people that this is all a big conspiracy by enemy states. But when your own prime minister defects and you are forced to say he was sacked, it’s a diversion from the propaganda line.”

“It’s humiliating,” she added.

Hijab’s spokesman, Otri, told one Arab broadcaster he would arrive in Qatar “within days.”

Opposition figures claimed members of the Free Syrian Army had coordinated the defection, which they said had been planned for some months.

SNC member Khalid Zein al-Abedin said Hijab, several members of his family, two ministers and three army officers crossed into Jordan after “coordination between the Syrian opposition and Free Syrian Army.”

News of the defection came as the Syrian army prepared a major ground assault against rebels in the northern city of Aleppo.

It also came as a bomb blast struck the Syrian state television headquarters in central Omayyad district of Damascus, wounding several people.

There was violence elsewhere around the capital, where rebels claimed government shelling had killed three of 48 Iranians they have been holding since Saturday. The rebels threatened to kill the other captives if the army did not halt its bombardment.

In Aleppo, the army bombarded a string of rebel neighborhoods after government security officials said troops had completed their build-up and that a 20,000-strong force was poised for a ground assault.

A rebel commander was killed in the Salaheddine district in the southwest, and troops shelled the Palace of Justice as well as the Marjeh and Shaar districts, the Britain-based Syrian Observatory for Human Rights said. At least 10 people were killed in Aleppo Monday, among them eight civilians, the observatory said.

In all, the observatory said at least 91 people had been killed in violence across the country.

Rebels have tried to overrun Damascus and Aleppo, but have been largely outgunned by the Syrian army’s superior weaponry.

U.N. observers have been moved out of the city of Aleppo because of worsening security, a U.N. spokeswoman said Monday. The head of the U.N. Supervision Mission in Syria, Lt. Gen. Babacar Gaye issued an appeal on behalf of civilians, amid fears of a looming bloodbath there.

“I urge the parties to protect civilians and respect their obligations under international humanitarian law. Civilians must not be subjected to shelling and use of heavy weapons,” Gaye said. – With agencies