Around 40 students were in the bus that was headed to the army-run school, Iqbal said, adding that several were injured in the incident.

The vehicle was carrying dozens of children to a military-run school in southwestern Balochistan Province, a region long roiled by rebel activity.

No group immediately claimed responsibility, though suspicion is likely to fall on ethnic Baloch separatists, who frequently target security forces and civilians in the region.