Two suicide bombers blasted two security centers in central Damascus Friday, leaving about 30 people dead and over 100 others injured, a senior local official said.

This is the worst violence that hit the unrest-torn country since protests against President Bashar al-Assad erupted in mid- March.

The sound of explosions rattled Damascus Friday as wailing sirens could be heard at the nearby al-Mazzeh neighborhood. Ambulances were rushing towards the military hospital in al-Mazzeh.

A government official confirmed to Xinhua that there had been two explosions Friday.

Syria's state TV said the attackers were driving two cars with bombs, adding that initial investigations show al-Qaida group behind the explosions.

The TV said the first attack was carried out against the headquarters of the State Security Department and the other hit one of the security branches, labeling the incidents as "terrorist act."

The private-Sham FM said most of the centers' guards were killed, adding that big material damages were caused.

The bombing came as the Arab League (AL) observers have arrived in Damascus to monitor the country's unrest on ground.

Syria said Thursday that more than 2,000 army men have been killed by armed groups since the unrest began in March.