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.
Other soldiers also exposed to the gas in the cave have been taken to the hospital for treatment, the ministry said.
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).
Turkey's pro-Kurdish party will meet with President Erdogan
Turkey's pro-Kurdish DEM party will meet President Tayyip Erdogan also on Monday, seeking to move along a peace process between the Turkish state and the Kurdistan Workers Party (PKK) militant group.
DEM, the country's third-biggest party and which has played a key role facilitating the PKK's disarmament decision in May, said it met PKK leader Abdullah Ocalan in prison on Sunday.
"(Ocalan) he said he attaches great importance to our delegation's meeting with the president, described it as historic," the party said in a statement.
The PKK, which has been locked in a bloody conflict with the Turkish state for more than four decades, decided in May to disband and end its armed struggle. The PKK could start handing over its weapons in the coming days, officials and sources said.
President Erdogan will receive DEM Party leaders and a delegation in Ankara at 1200 GMT. They are expected to discuss the recent developments in the PKK disarmament process.
Since Ocalan's public call to his PKK in February, DEM has held talks with Erdogan and other government officials seeking to propel the potential peace process.
Since the PKK launched its insurgency against Turkey in 1984 - originally with the aim of creating an independent Kurdish state - the conflict has killed more than 40,000 people, imposed a huge economic burden, and fueled social tensions.