ISTANBUL — Turkey said Sunday that 13 Turkish hostages, including soldiers and police officers, held by a Kurdish militant group had been found executed in a cave in northern Iraq.

The bodies were found during a Turkish military operation against the Kurdistan Workers’ Party, or PKK, that began last week, according to a Defense Ministry statement. The ministry did not say exactly when the bodies were discovered or whether the executions had occurred during a rescue attempt. All but one of the victims was killed with a bullet to the head, the ministry said.

Many of the hostages had been kidnapped in Turkey in the summer or spring of 2015, after the breakdown of a cease-fire between the government and the PKK, which has fought a decades-long insurgency against Turkey, according to a statement by the governor of Turkey’s Malatya province that was carried by the state-run Anadolu news agency. It was the worst loss suffered by Turkey’s security services since last February, when 36 Turkish troops were killed in a suspected airstrike in Syria’s Idlib province.

A statement Sunday by the PKK did not deny that the group was holding Turkish prisoners but blamed the deaths on Turkey, saying its attack on a prisoner camp resulted in clashes that killed captives who belonged to Turkey’s intelligence service, along with soldiers and police officers.

President Recep Tayyip Erdogan’s government has carried out large-scale military operations against the PKK in Iraq and Syria over the past few years that it says are aimed at protecting Turkey from cross-border attacks. They included a major incursion into northern Syria in 2019 that targeted Kurdish-Syrian fighters who were allied with the United States.

The latest Turkish operation, which began Wednesday, has focused on a region north of the Iraqi city of Dahuk. The Defense Ministry said three Turkish soldiers have died and dozens of Kurdish fighters were killed or captured during the campaign.

The military campaigns have coincided with a crackdown on pro-Kurdish voices inside Turkey, including on media outlets and politicians whom the government has accused of supporting the PKK, which Turkey and the United States have designated a terrorist group. Human rights groups have accused the Turkish government of using its fight against the PKK to silence dissenters, including members of a pro-Kurdish opposition party.

Fahrettin Altun, a spokesman for Erdogan, said in a statement on Twitter that Turkey would “continue its fight against terrorism with unwavering determination” and would “take necessary steps against individuals and groups glorifying and encouraging terrorism at home and abroad.”