The clashes, which took place close to Umayyad Square in the heart of the Syrian capital, were the first such next to a public building in Damascus since the standoff between the authorities and the banned Muslim Brotherhood in the 1980s.

"Special security forces thwarted early today a terrorist operation that targeted uninhabited buildings behind the building of the (state) radio and television," the Syrian state news agency Sana said.

"Four members of the terrorist group were killed in the clashes, two were wounded and four captured," the news agency said. "A security guard was killed in the exchanges and two others were wounded."

The abandoned buildings targeted by the militants are close to an office of Syrian customs just behind Umayyad Square, which houses several public buildings including the national library and national opera.

Syrian army headquarters are also in the vicinity.

Interrogations of the arrested suspects have commenced and an inquiry has been opened, Sana said.

The agency described the attackers as being from a "terrorist and extremist group" but did not offer any indication as to their identity.

"Security forces confiscated arms including ten rifles manufactured in the United States and locally-made grenades as well as recordings of religious sermons," an interior ministry statement added.

The first elements of the inquiry show that "the arms were sent from a neighbouring country to carry out acts of sabotage against objectives of vital interest," it added.

The site of the early morning clashes had returned to calm by midafternoon, with traffic flowing easily on the main day of rest in Syria.