Twelve Turkish soldiers have died after being exposed to methane gas while searching a cave in northern Iraq, the Turkish Ministry of National Defence said.

At least 19 personnel were exposed to the gas during the search and clear operation on Sunday, and immediately taken to hospital. By Monday, 12 had died, the ministry said.

President Recep Tayyip Erdogan said he received the news with ?great sorrow? and extended his condolences to the soldiers? families and to the Turkish Armed Forces.

Methane gas is not directly toxic, but can be deadly as it can become suffocating, especially in tight, enclosed spaces.

It remains unclear why the cave contained enough methane gas to make it lethal.

A farewell ceremony for some of the soldiers killed was held at an airport in the southern Turkish province of Hakkari on Monday. It was attended by the Turkish defence minister and many high-ranking officials from the armed forces.

The bodies were then transported back to the their home towns.

The soldiers were searching for the body of a soldier who was killed in gunfire in May 2022 during Operation Claw Lock ? a military operation led by Turkey against militants from the Kurdistan Workers? Party (PKK) in Iraq which included air strikes on caves as well as a ground incursion.

The PKK - which is banned as a terrorist group in Turkey, the EU, UK and US ? has waged a 40-year insurgency against Turkey.

The group?s initial aim when it began fighting with Turkey in the 1980s was to create an independent home for Kurds. It then moved away from its separatist goals, focusing instead on more autonomy and greater Kurdish rights.

Over the last four decades more than 40,000 people have been killed in the conflict.

In March, the PKK declared a ceasefire and in May said it would disband, stating it had ?completed its historical mission? and would ?end the method of armed struggle.?

In the first significant step towards peace since the announcement, the PKK said a group of fighters will lay down arms this week in Iraqi Kurdistan. (BBC, excluding headline)

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