QUETTA, Pakistan (AP) — A powerful bomb targeting government soldiers exploded at a coal mine in southwest Pakistan, killing four soldiers, the military said Monday.

The attack happened at Marget Mines, about 75 kilometers (45 miles) east of Quetta, the capital of Baluchistan province, a statement released by the military said.

It said the slain soldiers were guarding the coal mine and a search operation was still underway to track and arrest those who orchestrated the attack.

No one claimed responsibility but militants and separatists have previously attacked coal miners and security workers in the region and elsewhere. Pakistan has deployed troops to ensure the protection of coal mines and oil workers in the region.

Baluchistan has for years been the scene of a low-level insurgency by small separatist groups who complain of discrimination and demand a fairer share of their province’s resources and wealth, such as natural gas and mines. The Pakistani Taliban and the Islamic State group also have a presence.