Syria's Prime Minister Riyad Hijab has defected with his family to Jordan, according to state television.

His spokesman Mohammed el-Etri told al-Jazeera TV that he was in a safe location, poised to "join the revolution".

News of the defection surfaced as a bomb blast destroyed the third floor of the Syrian state TV building in Damascus, wounding three employees, Syrian TV said.

The ex-agriculture minister was appointed prime minister by President Bashar al-Assad following a parliamentary election in May.

The Syrian Observatory for Human Rights, Al-Jazeera journalist Faisal al-Qassem and other opposition sources reported that the sacked PM had defected to Jordan along with three other ministers.

HIjab is the second former chief of the Baath Party branch in Deir Ezzor to defect, after Nawaf al-Fares.

Assad has already appointed Omar Ghalawnji, minister of local administration in Syria, to lead the temporary caretaker government.

The bomb blast hit the principal media outlet for government's account for fighting against rebels. In late June, a gunman stormed a pro-government station in the capital, killing seven employees and ripping its studios with explosives.

Severe security breach

The TV remained on air despite what was another severe breach of a state institution in a heavily guarded area. In July, a blast in the National Security HQ in the Damascus killed four close security aides of embattled president Bashar al-Assad, including the defence minister Daoud Rajiha and Assad's brother-in-law Assef Shawkat.

Footage of the latest blast by pro-government private Syrian TV station Al-Ikhbariya showed toppled walls, overturned desks, blown-out cabinet doors, broken glass and dangling electricity cables.

Information minister Omran al-Zoubi blamed Qatar, Saudi Arabia and Israel for the attack.

"Nothing can silence the voice of Syria or the voice of the Syrian people," al-Zoubi said while inspecting the damage at the TV building. "We have a thousand locations to broadcast from."

Meanwhile, Iran has strongly denied that 48 of its citizens taken hostage by Syrian rebels are Revolutionary Guards, claiming they were religious pilgrims.

"They are Iranian thugs who were in Damascus for a field reconnaissance mission," said a rebel leader in a video.

In the footage, the rebels branded what they said were Iranian id cards and certificates for carrying weapons proving that the hostages were not pilgrims.

Iranian media said the 48 were seized from a bus in Damascus, the latest in a string of kidnappings of visitors from the Islamic Republic. The Iranian embassy in Damascus said they had travelled to Syria using a private tour company for a pilgrimage to the Shiite shrine of Sayyida Zeinab, in southern Damascus.

Iran's foreign minister Ali Akhbar Salehi contacted the Syrian and Turkish foreign ministries, asking them to secure the release of the Iranians.

But Syrian rebels said consultations were stalled.

"Negotiations with parties inside or outside Syria are not open yet before we confirm the identity of the Iranians and prove that Iran is active on Syrian lands with its soldiers and arms," Capt Abdel Nasser al-Shumair, commander of the al-Baraa brigade of the Free Syrian Army, told Dubai-based al-Arabiya television.