More than 40 people were killed in twin suicide bombings that targeted two government buildings in Damascus, Syrian Deputy Foreign Minister Faisal Meqdad said.
"There are more than 40 dead and more than 100 wounded in today's two attacks," Mr Meqdad told reporters at the site of one of the bombings.
"On the first day after the arrival of the Arab observers, this is the gift we get from the terrorists and al Qaeda," he said, referring to the Arab League mission designed to end nine months of bloodshed.
"But we are going to do all we can to facilitate the Arab League mission," he added.
"The terrorists wanted the first day of the observer mission in Damascus to be a tragic day, but the Syrian people will stand strong in the face of the killing machine, supported by the Europeans, the Americans and some Arab countries," he said, alluding to Western support for the opposition.
The attacks targeted the General Security Directorate and another security branch in the city, the state news agency SANA said in its report.
"Preliminary investigations indicated that that the criminal attack carries the blueprints of al Qaeda," SANA said.
Rescue efforts were underway as video footage of damaged and burnt buildings were broadcast on state TV.
Graphic photos of civilian casualties were also posted on SANA's website. Civilians bore the brunt of the attacks, though some soldiers were also killed and the death toll is expected to rise.
One of the suicide bombers was actively trying to target the building that houses the General Security Directorate, authorities said.
Opposition activists have accused the government of staging the attack, which took place just a day after the Arab League monitoring team arrived.