Syria's official news agency says one person was killed when a bomb exploded on a footbridge in central Damascus.
The blast happened less than a kilometre from a hotel where anti-government groups had gathered for a rare meeting.
Foreign diplomats were present to hear strongly-voiced calls for a peaceful solution to the crisis.
A spokesman for the National Development Party urged the UN-Arab envoy Lakdhar Brahimi to push for an international conference on Syria, to pave the way for a peaceful transition to democracy.
The groups form a bloc effectively sanctioned by the Assad regime.
Brahimi is due before the UN Security Council on Monday to give his first assessment on Syria since taking on the role.
