Three members of the Iraqi security forces were killed in an explosion north of Baghdad on Wednesday, Iraq’s military said.

The personnel were killed when an explosive device detonated during a security operation in the Khan area of the Tarmiyah district. A commander of the 59th Infantry Brigade and two others were killed, a military statement said.

Lt. Gen. Qais al-Muhammadawi, commander of Iraq’s ground forces, will lead an investigation in the area into the causes of the explosion, the statement added.

The perpetrators were not immediately known. The Tarmiyah district has witnessed numerous attacks by the Islamic State group since Iraqi security forces with assistance from the U.S.-led coalition drove out the group in a military operation.

IS’s territorial control in Iraq and Syria was crushed by the years-long campaign, but sleeper cells have carried out attacks that have killed scores of Iraqis and Syrians.

In Iraq, the militants have successfully exploited security gaps across a patch of territory in the north because of an ongoing dispute between Baghdad and Irbil, the capital of the the Kurdish-run semi-autonomous region of Iraq. Iraqi security forces have been ambushed or targeted with improvised-explosive devices by the militants.

AP