ANKARA, Turkey (AP) — A small plane belonging to Turkey’s police force has crashed into a mountain in eastern Turkey, killing seven security personnel on board, Turkey’s interior minister said Thursday.

The plane was returning from a surveillance and reconnaissance mission late Wednesday, when it crashed into Mount Artos at an altitude of 2,200 meters (some 7,200 feet), Suleyman Soylu told reporters. The mountain, a dormant volcano, is situated in Van province, near the border with Iran.

The minister, who traveled to the region to oversee the recovery operation, said the plane disappeared from the radar on its way back to Van's Ferit Melen Airport. The plane’s wreckage was found at around 3 a.m. (0000 GMT), he said.

All on board, including the two pilots, were members of the national police.

The cause of the of crash was under investigation, Soylu said.

The plane was on a surveillance mission over Van and the neighboring, mostly Kurdish-populated province of Hakkari, which lies farther south and borders both Iran and Iraq.

Turkish security forces are engaged in operations against rebels belonging to the outlawed Kurdistan Workers Party, or PKK, in the region, but it was not immediately clear if the surveillance mission was linked to security operations against the militant group.

The PKK, which has waged a more than three-decade-long insurgency, is considered a terror organization by Turkey, the United States and the European Union.