Five nuclear scientists are reported to have been killed by unidentified assailants in the Syrian capital Damascus.

The nuclear engineers were travelling in a bus in northern Damascus near a research centre when they were attacked, said a monitoring group.

Rami Abdel Rahman, the chief of Britain-based Syrian Observatory for Human Rights (SOHR), told AFP: "Unidentified attackers murdered five nuclear energy engineers who worked in the scientific research centre near the neighbourhood of Barzeh, northern Damascus.

"It was not immediately clear whether the bus that they were travelling on was hit by a bomb, or by gunfire."

The monitoring group which collects information from the war-torn Syria through a network of sources including locals and informants was unable to identify the nationalities of the scientists.

Unconfirmed reports suggest the engineers, four of them Syrians and one Iranian, were shot dead.

Syrian government officials have not commented on the incident as yet.

Rebels fighting against President Bashar al-Assad's regime earlier carried out a similar attack near the same facility, believed to be directly linked to Assad's Ministry of Defence, in July 2013 killing six officials.