A pro-government Syrian newspaper and a monitoring group say that militants opened fire on a bus carrying nuclear scientists and engineers near Damascus, killing at least four men.
The Watan newspaper said on Monday that the men were heading to work at the Scientific Research Center near the Syrian capital when they were attacked Sunday.
The newspaper says the four victims were Syrian nationals, and suggested al-Qaida-linked militants were responsible for the attack.
Rami Abdurrahman of the Syrian Observatory for Human Rights said five nuclear engineers were killed and that one of the men was an Iranian national.
The Britain-based Observatory closely monitors Syria's fighting through a network of activists on the ground.
Conflicting reports following such incidences is routine.
There was no immediate comment by Syrian officials.