Five Turkish soldiers have died after being exposed to methane gas while searching a cave in the Kurdistan region for the remains of a fellow soldier killed by the PKK in 2022, the Turkish Defense Ministry announced on Sunday.

According to the ministry, 19 soldiers were inside the mountain cave when they were exposed to methane gas, which is colorless, odorless, highly flammable, and can cause asphyxiation at high concentrations.

“They were immediately transported to hospital, but despite all interventions, five heroic personnel died,” the statement said. Rescue operations in the area are ongoing.

The ministry did not specify the exact location of the incident but said it occurred within the “Claw-Lock Operation region,” referring to Turkey’s ongoing military operation against the Kurdistan Workers’ Party (PKK) launched in April 2022.

The unit affected by methane was searching for the remains of an infantry officer who was killed by “terrorist gunfire” during a search-and-clear mission in May 2022. Teams have been attempting to recover his body for the past three years.

The cave, situated at an altitude of 852 meters (2,795 feet), was previously used as a PKK hospital before being cleared by Turkish forces. President Recep Tayyip Erdogan’s office said the soldiers were exposed to a “high concentration of accumulated methane gas.”

In May, the PKK announced plans to disband and renounce armed conflict as part of a new peace initiative with Turkey. Its fighters are expected to begin surrendering their weapons in the coming days as the first step toward disarmament.