ANKARA, Turkey — Seven more Turkish soldiers have died from methane gas poisoning following a cave search operation in northern Iraq, Turkey’s Defense Ministry said Monday, bringing the death toll to 12. The soldiers had been searching for the remains of a fellow soldier previously killed by Kurdish militants.

The troops were searching a mountain cave when 19 of them were exposed to the gas, according to the ministry. Five of the soldiers died Sunday from the colorless, odorless, flammable gas that can cause asphyxiation in sufficient concentration, and seven more succumbed on Monday.

“We pray for God’s mercy upon our heroic martyrs who lost their lives in this tragic event,” the ministry said Monday.

It said Defense Minister Yasar Guler and armed forces’ commanders were traveling to the region to carry out “inspections and evaluations” and attend a ceremony. Speaking at the ceremony, Guler commended the troops’ “great courage and sacrifice,” adding: “Our grief is immense and our feelings are beyond words.”

— The Associated Press