ANKARA, Turkey (AP) — A sudden, mid-flight change of weather conditions is thought to be the cause a helicopter crash which killed 11 military personnel in eastern Turkey, the Defense Ministry said Friday, citing a preliminary inspection of the crash site.

The Cougar army helicopter went down on a snow-covered area close to the village of Cekmece, in the predominantly Kurdish-populated Bitlis province on Thursday. The victims included Lt. Gen. Osman Erbas, an army corps commander.

Two military personnel survived the crash with injuries.

The Defense Ministry statement said an initial inspection of the wreckage showed no evidence of an explosion or fire. There was also no meteorological warning prior to the flight, it added.

“In the light of the initial information, it is considered that the accident occurred due to adverse weather conditions that occurred as a result of a sudden change in weather conditions in the region,” the statement read.

The ministry added that a more detailed technical inspection would determine the definitive cause.

The location of the crash is in an area where Turkish troops have been combating militants of the banned Kurdistan Workers’ Party, or PKK, which is considered to be a terrorist group by the United States and the European Union. The conflict has killed tens of thousands of people since 1984.

In 1997, PKK militants attacked a Turkish Cougar helicopter in northern Iraq, killing 11 Turkish soldiers.

More recently, 13 military personnel were killed in 2017, when a Cougar helicopter crashed into power lines shortly after take-off from a base near Turkey’s border with Iraq.