Four oil facility guards were killed in an attack on a bus on a highway east of Syria's Deir al-Zor.

Axar.az informs, citing Reuters, no group immediately claimed responsibility for the attack.

The military personnel, part of an army contingent securing the Teim oilfield, were returning home after their shift at the major site west of Deir al-Zor province, when their vehicle was hit near the town of Salo on the highway east of Deir al-Zor, a security source told Reuters.

The incident is the deadliest since Assad’s fall in the eastern province, which produces most of Syria’s oil and wheat. Three months ago, ISIS sleeper cells attacked a police station in Mayadeen.