“Unidentified attackers murdered five nuclear energy engineers who worked in the scientific research center near the neighborhood of Barzeh, northern Damascus,” said Observatory director Rami Abdel Rahman. AFP reports that four of the atomic engineers were Syrian, while the other one was Iranian.

“Their bus was ambushed while they were on their way to the research centre. Their assailants shot them dead," Rahman said. So far no one has claimed responsibility for the attack. This is not the first time that Syrian scientists have been deliberately targeted. A military research center was hit by a deadly Israeli raid in May 2013.

Shortly thereafter, workers at the Scientific Research Center in Barzeh were targeted by a group of jihadists who shot an RPG at their commuter bus on July 31, 2013. Six workers were killed and 19 injured.

Nuclear Threat Initiative (NTI), a non-partisan, non-profit organization, says that Syria is a non-nuclear weapon state party to the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) since 1969.

The UN International Atomic Energy Agency (IAEA) said last year that Syria had declared a “small amount of nuclear material,” most probably highly enriched uranium, used in a Miniature Neutron Source research reactor, near Damascus, according to Reuters.

Damascus is currently known to possess only one small operational research reactor, the Chinese built SRR-1, which is used for research on peaceful energy needs.

The Atomic Energy Commission of Syria (AECS) directs Syria's nuclear program, and most of Syria's nuclear-related work is done at the Der Al-Hadjar Nuclear Research Center and the Scientific Studies and Research Center (SSRC) in Damascus.