A second suicide bombing hit the Syrian capital Damascus on Wednesday, causing deaths and injuries, after an attack at a central courthouse killed at least 25 people, state media reported.

"A terrorist blows himself up with an explosive belt inside one of the restaurants in the Rabweh area in Damascus causing a number of deaths and injuries," state news agency SANA reported.

The restaurant blast in the west of the city came less than two hours after the first suicide attack at a central courthouse in the Hamadiyeh neighbourhood.

The attacks come as Syria marks the sixth anniversary of its brutal conflict, which began with anti-government protests in March 2011 and has killed more than 320,000 people.