A crew member checks a U.S. Air Force C-17 at the airport in Irbil.

Iraq’s Defense Ministry was not informed about a joint U.S. and Kurdish military operation that rescued 69 prisoners held by ISIS , a ministry spokesman said on Friday.

“We just heard this from the media, we didn’t know about it,” General Tahsin Ibrahim Sadiq told Reuters.

“It was just the peshmerga (Kurdish forces) and the Americans, and the Ministry of Defense didn’t have any idea about that.” Sadiq said ministry officials were meeting representatives of the U.S.-led coalition in Baghdad on Friday to learn more about the operation, the most significant raid against ISIS in months.

Initial reports said Thursday’s operation near the northern town of Hawija had freed Kurdish hostages, but officials later confirmed the detainees were Arabs, including around 20 members of the Iraqi security forces. The others were local residents and ISIS fighters that the group had accused of spying, said a U.S. official.

The prisoners were about to be executed and dumped in four mass graves, the official said.

ISIS holds hostages in similar detention centers across the sprawling lands it controls in northern Iraq and neighboring Syria.

The extremist group also regularly executes people it accuses of various crimes including spying for the Iraqis or foreign powers.

It was not immediately clear why these particular hostages triggered a potentially risky rescue mission.

Long-standing enmity between Arabs and Kurds, who aspire for greater autonomy in their northern region, have complicated efforts to unify the battle against ISIS militants.

During a recent visit to Iraq, U.S. Marine General Joseph Dunford, chairman of the Joint Chiefs of Staff, called for changes to Iraq’s fragmented security structure.

The security forces are now divided, with different commanders speaking to the United States on behalf of Iraq’s army, its militias, police and Kurdish peshmerga.

A CIA spokesman declined to comment on the suggestion that the rescued hostages had connections to the U.S. government. The Pentagon’s press secretary said the operation did not mark a change in U.S. tactics in the war on ISIS militants.

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