Syrian army defectors attacked an intelligence complex on the edge of Damascus early on Wednesday morning, according to a report by the Reuters news agency.
It was the first reported assault on a major security facility in the eight-month uprising against President Bashar Assad, according to activists.
The activists told Reuters that members of a group calling itself the Free Syrian Army fired shoulder-mounted rockets and machine guns at a large Air Force Intelligence complex situated on the northern edge of the capital, on the Damascus-Aleppo highway at about 2:30 a.m. local time.
A gunfight ensued and helicopters circled the area, the sources said, adding that there was no immediate report of casualties and the area where the fighting occurred remained inaccessible.
Reuters noted that together with Military Intelligence, Air Force Intelligence is in charge of preventing dissent within the army. The two divisions have been instrumental in the crackdown on the uprising against Assad, which the United Nations says has killed 3,500 people.
Some have speculated that the only way that Assad could be toppled is if his soldiers defect in large numbers. An Arab official told Reuters that while insurgent attacks on loyalist forces rose sharply in the last 10 days, the army remains largely cohesive.
On Monday, Syrian forces murdered 70 protesters, including 12 suspected army deserters, as Assad continued to be isolated. On Saturday, the Arab League suspended Syria, essentially leaving Assad with Iran and Lebanon, which Damascus effectively controls, as his only regional allies.
Syria's foreign minister Walid al-Muallem later condemned the Arab League's decision, saying the move would be "illegal" and a "dangerous step". He said that the decision was "illegitimate" and had been prompted by US incitement.