Harmony Gold Mining has said it suspects illegal miners planted explosives at its Phakisa mine in South Africa, which might have led to an explosion that killed four people.

Last week Harmony suspended mine operations after an underground explosion at the Phakisa mine.

Harmony spokesperson Marian van der Walt said employees found “booby trap explosives” in the mine while fixing ventilation systems.

The company suspects a booby trap found underground could have caused a fire which then led to the explosion.

Van der Walt added it was too soon to conclude that criminal miners were the cause of the explosion, according to Reuters.

South African police and the Department of Mining have launched investigations into the accident.