Twelve Turkish soldiers died after being exposed to methane gas during a search operation in a cave in northern Iraq, the defense ministry said on Monday.
In a statement, the ministry said the incident took place on Sunday during a mission to locate the remains of a Turkish soldier killed during a military operation against the outlawed Kurdistan Workers Party (PKK).
Other soldiers who are also exposed to the gas in the cave have been taken to the hospital for treatment, the ministry said.
The cave was at an altitude of 852 meters (2,795 foot) and was known to have been used as a hospital by the PKK in the past, although it had since been cleared by Turkish soldiers.
Türkiye and the PKK have waged a 40-year conflict which has often spilled over into Iraq and Syria. Türkiye has set up a series of bases in northern Iraq, where the PKK has been established for decades.