Four Syrian soldiers were killed when their bus was ambushed near the Teim oilfield in Deir al-Zor, a region long plagued by insurgent activity.
According to security sources, the attack targeted troops guarding the oil facility as they travelled home along a stretch of road frequently used by military convoys.
No group has claimed responsibility, but ISIS sleeper cells remain active in the area and have carried out similar strikes in recent months.
The assault underscores the ongoing instability in eastern Syria despite years of counterterrorism operations.