Unknown assailants killed five nuclear engineers Sunday while they were on a bus just north of Damascus, near the research center where they worked, a monitor said on Sunday.
The Britain-based Syrian Observatory for Human Rights, which relies on a network of sources on the ground for its reports, was unable however to say how they were killed or supply their nationalities.
"Unidentified attackers murdered five nuclear energy engineers who worked in the scientific research centre near the neighbourhood of Barzeh, northern Damascus," said Observatory director Rami Abdel Rahman.
"It was not immediately clear whether the bus that they were travelling on was hit by a bomb, or by gunfire," Abdel Rahman told AFP.
In July last year, six people who worked at the same center were killed in a mortar attack carried out by rebels seeking President Bashar al-Assad's ouster.
Another military research center, also near Damascus, was also hit by a deadly Israeli raid in May 2013.