A bomb attached to a motorcycle has exploded near Syria's Interior Ministry and intelligence headquarters in Damascus, causing an unspecified number of casualties.
There are conflicting reports about whether the attack on October 18 was carried out by a suicide bomber.
The blast comes after opposition activists said government airstrikes on rebel areas overnight killed at least 20 people in four towns in the Idlib and Aleppo provinces.
Meanwhile, the activist group Avaaz said on October 18 that some 28,000 Syrians have gone missing after being abducted by forces loyal to President Bashar al-Assad during the country's 19-month revolt.
Navi Pillay, the UN High Commissioner for Human Rights, said in Geneva on the same day that the conflict in Syria is becoming reminiscent of Bosnia's sectarian war.
Pillay called on world powers to unite to try to halt the bloodshed.
Based on reporting by Reuters,dpa, and AFP