Hijab's spokesman said he was joining the rebels in protest at the ''genocide'' President Bashar al-Assad has instigated against his own people.

"I announce my defection today from the regime of killing and terror, and I join the ranks of the revolt," Hijab said in a statement read on Al-Jazeera satellite TV yesterday from Amman, Jordan.

His defection came at a time, he said, "when Syria is passing through the most difficult war crimes, genocide and barbaric killings and massacres against unarmed citizens".

The statement said Hijab was at a "safe haven" with his family.

A government source in Jordan said he had fled there.

Hijab was appointed prime minister on June 23. The state TV report did not say why Hijab was dismissed.

It said Omar Ghalawanji, Hijab's deputy, had been named as his temporary replacement.

Hijab, a Sunni Muslim, was a ruling Baath Party apparatchik.

The US said the defection showed that Assad's people believe his days are numbered.

"Today's reports that senior members of the Assad regime, including Prime Minister Hijab, have defected are the latest indication that Assad has lost control of Syria and that the momentum is with the opposition forces and the Syrian people," US National Security Council spokesman Tommy Vietor said.

The announcement came hours after a bomb ripped through the third floor of the state TV building in Damascus, causing heavy material damage and light injuries.

In Syria's commercial capital, Aleppo, the army bombarded a rebel neighbourhood after government security officials said troops had completed their build-up and a 20000-strong force was poised for a ground assault.