CNN reported one American was killed during the operation.

One member of a U.S. special operations force was killed during an overnight mission to rescue hostages held by ISIS militants in northern Iraq, the first American to die in ground combat with the militant group, U.S. officials said on Thursday.

Sixty-nine hostages were rescued in the action, which targeted an ISIS prison around 7 kilometers north of the town of Hawija, according to the security council of the Kurdistan region, whose counterterrorism forces took part.

The hostages rescued in the raid were all Arabs, including local residents and ISIS fighters held as suspected spies, a U.S. official said on Thursday.

The official told Reuters that around 20 of the hostages were members of Iraqi security forces.

“Some of the remainder were Daesh (ISIS) … fighters that Daesh thought were spies,” the official said. “The rest of them were citizens of the local town.”

More than 20 ISIS militants were killed and six detained, the security council said.

“Dozens” of U.S. troops were involved in the mission, a U.S. defense official said, declining to be more specific about the number.

“It was a deliberately planned operation, but it was also done with the knowledge that imminent action was needed to save the lives of these people,” the U.S. defense official said.

The U.S. serviceman was shot during the mission and taken to the Kurdistan regional capital Erbil, where he died, the U.S. defense official said. He was the first American serviceman killed in ground combat in Iraq since the United States withdrew its forces in 2011.

Pentagon press secretary Peter Cook said in a statement that those rescued included 20 members of Iraqi security forces. He said the mission had been requested by the Kurdistan Regional Government.

The Kurdish Security Council said the rescued hostages had been handed over to “relevant authorities” after receiving medical care.

Sources in the Hawija area said they heard blasts and gunfire overnight and that ISIS militants had withdrawn from view after the raid, apparently relocating their bases.

Five U.S. helicopters launched from Erbil were involved in the mission, and the United States was providing helicopter lift, intelligence support, air strike support, and advisory support to the peshmerga, the U.S. defense official said.

Air strikes were launched before and after the mission to block approaches to the prison and destroy it afterward, the U.S. defense official said.

The operation in the north was the most significant raid against ISIS since May, when American special operations forces killed one of its senior leaders, Abu Sayyaf from Tunisia, in a raid in Syria.

Hawija is a stronghold of ISIS militants who have captured several dozen Kurdish peshmerga fighters in battle.

ISIS, also known as ISIS, has been for more than a year the target of daily air strikes in Iraq and Syria by a U.S.-led coalition for more than a year.

The U.S. rescue mission unfolded amid mounting concerns in Washington over increasing Russian intervention in the Middle East.

Former Cold War foe Russia has been conducting airstrikes in Syria against opponents of its closest regional ally Bashar al-Assad, as Iraq questions American resolve to fight militants on its soil.

Russia has also joined a Baghdad-based intelligence cell along with Iran, Iraq and Syria that has provided information on ISIS targets.

Iraqi Prime Minister Haider al-Abadi faces intense pressure from the ruling coalition and powerful Shiite militias to request Russian air strikes on ISIS, which controls a third of the major OPEC oil producer.

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