The incident comes at a sensitive time, with Turkey in talks to end the conflict with the Kurds after the PKK militant group agreed to halt its decades-long armed struggle.

The conflict, which began in 1984, has cost more than 40,000 lives.

The deaths occurred when the Turkish troops were searching for the remains of a soldier who was shot dead by Kurdish fighters in the area in May 2022 and whose body was never recovered, Turkey's defence ministry said.

"Four other of our heroic comrades in arms, affected by methane gas, have died... bringing the total number of victims to 12," the ministry said on X on Monday.

It did not explain the origin of the methane gas in the caves.

"During a search operation in a cave... previously known to have been used as a hospital... 19 of our personnel were exposed to methane gas," the ministry said on Sunday.

When the soldier whose body the troops were looking for died in 2022, Turkey was waging Operation Claw Lock, with its troops seeking to eradicate Kurdish PKK militants holed up in caves along the border.

News of the deaths emerged as a delegation from the pro-Kurdish DEM party was visiting jailed PKK founder Abdullah Ocalan as part of the ongoing negotiations with the Turkish government.