Syria's state news agency says a bomb has gone off in a suburb southwest of the Syrian capital.

Thursday's blast comes as rebels seeking to oust President Bashar Assad have been edging closer to Damascus, his seat of power.

The SANA news agency did not give any casualties or provide further details about the bombing in Qatana suburb. The regime blames such bombings on "terrorists," its shorthand for rebel fighters.

On Wednesday, three bombs collapsed walls of the Interior Ministry buildings in Damascus, killing at least five people.

Rebels have been making gains against government forces in the capital's suburbs though most of the city is still beyond their reach.

Anti-regime activists say more than 40,000 people have been killing since the start of the anti-Assad uprising in March 2011.