An Iraqi official says mass graves found in an area recently retaken from the Islamic State group could contain up to 400 bodies.

Kirkuk governor Rakan Saed said Sunday that the bodies of civilians and security forces have been found in an abandoned base near Hawija, a northern town retaken in early October.

Khalaf Luhaibi, a local shepherd who led troops to the site, says IS used to bring captives to the area and shoot them dead or pour oil over them and light it on fire. The area was strewn with torn clothing and what appeared to be human bones and skulls.

Iraqi forces have driven IS from nearly all the territory it once controlled. Authorities have already uncovered several mass graves in other newly liberated areas.