A "huge explosion" near a military intelligence office in Damascus Sunday left a number of dead and wounded, a war monitor said, after the state-run news agency Syrian Arab News Agency (SANA) said early reports suggested a "terrorist act".

"The explosion took place near a security branch in the south of the city. There are some people killed and injured but we could not verify the toll immediately," the Britain-based Syrian Observatory for Human Rights told AFP.

It was unclear if the blast was caused by a bomb that was planted or a suicide attack, the monitor said, adding that shooting followed the explosion.

"Explosion heard around the southern highway in Damascus area, first reports suggest a terrorist act," SANA said.

SANA said all roads leading to the scene of the blast have been closed.

The state outlet did not provide any more details on the incident.