A car bomb killed a number of soldiers and wounded at least 20 others at an army checkpoint near a military airport in Damascus, the Syrian Observatory for Human Rights said.
"There are at least 20 soldiers wounded, there are also some dead but we don't know how many," said the Observatory.
The explosion, close to the Mazzeh military airport in the western suburbs of Damascus, was heard in several neighbourhoods in the capital and flames were visible from a distance, the Britain-based group said.
Director of the Observatory, Rami Abdel Rahman, said the airport was as big as the capital's international airport and was used by President Bashar al-Assad and other senior figures in his regime.
The military airport is guarded by the army's elite Fourth Division,which is responsible for security in and around Damascus. It is led by Assad's brother Maher al-Assad.
The last attack in the capital was on Tuesday, when when twin suicide bombers targeted a police station in the city centre killing at least 14 people and wounding more than 30 others.
A series of attacks have hit Damascus in recent months, most of them aimed at security check points, soldiers or government buildings.
On April 29, a car bomb exploded in Mazzeh targeting the car of Prime Minister Wael al-Halqi. He escaped unscathed but his bodyguards were killed.