Suicide car bombers struck Damascus on Friday, officials said, sending human limbs flying in the bloodiest violence in Syria's capital since a revolt against President Bashar Al-Assad began nine months ago.

An interior ministry spokesman raised the death toll to 44 people in an evening address on state television, blaming al Qaeda for the blasts which hit two security buildings.

They struck a day after Arab League officials arrived to prepare for monitors who will check whether Assad is implementing a plan to end the bloodshed. The first monitors will travel to Syria on Monday, Egypt's news agency said.

Assad has unleashed tanks and troops to try to crush nine months of street protests inspired by other Arab uprisings this year. Mainly peaceful rallies are now increasingly eclipsed by an armed insurgency against his military and security apparatus.

But Friday's blasts in central Damascus signalled a dramatic escalation in violence, which Syrian authorities blame on armed groups they say have killed 2,000 soldiers and security force members this year. The United Nations says Al-Assad's crackdown has killed 5,000 people.

"It's a new phase. We're getting militarised here," said Joshua Landis, a Syria expert at the University of Oklahoma who felt Friday's bombs were a "small premonition" of what may come in a country that some analysts see slipping towards civil war.

"This is when the Syrian opposition is beginning to realise they are on their own," he added, referring to Western reluctance to intervene militarily in Syria.

The interior ministry spokesman said 166 people were wounded by the explosions. It broadcast footage of mangled bodies being carried in blankets and stretchers into ambulances.

Bloodied streets were littered with human remains, blackened hulks of cars and a row of corpses wrapped in sheets.

"This is a qualitative escalation of the terrorist operations that Syria has been exposed to for the last nine months," the interior ministry spokesman said.

"These two suicide terrorist operations show, once again, the real face of the plot seeking to shake Syria's stability."

He said the first car bomb struck the main entrance of Damascus security branch at 10.18 am. The second bomb, one minute later, hit a central intelligence building.

Foreign Ministry spokesman Jihad Makdesi said the attacks were carried out by "terrorists (trying) to sabotage the will for change" in Syria, and followed warnings from Lebanon that al Qaeda fighters had infiltrated Syria from Lebanese territory.

The United States condemned the attacks, saying there was "no justification for terrorism of any kind" and that the work of the Arab League should not be hindered. – Reuters