An American soldier was killed in action in Iraq on Thursday for the first time since the renewed military intervention in the country last year, during a Kurdish and United States commando raid to free prisoners being held by Islamic State militants, the Pentagon said.
The raid, near the northern town of Hawija, freed about 70 prisoners but it was not the group the soldiers had expected to find, American and Iraqi officials said. American officials said that five Islamic State fighters had been detained and that important intelligence about the terrorist group had been recovered.
The raid was the first time American soldiers had been confirmed to be directly accompanying local forces in Iraq onto the battlefield against the Islamic State since President Obama sent troops back to the country last year.
Until now, the American contingent, which numbers around 3,500, had been limited to training and advising the Iraqi and Kurdish forces on military bases and training areas. But senior American military officials have long signalled that they might ask the White House for permission to send small teams into the field with Iraqi forces for some important operations, such as the battle for Mosul.
The Pentagon press secretary, Peter Cook, said the United States was trying to help a loyal ally - the Kurdish Regional Government - and was also rushing to save lives.
''This was a unique circumstance in which very close partners of the United States made a specific request for our assistance,'' he said. ''So I would not suggest that this is something that's going to now happen on a regular basis.''
It was not, Cook insisted, a forerunner of a more aggressive posture in which American troops would regularly join the Iraqis on combat operations.
The decision to use American helicopters to fly Kurdish commandos to Hawija, and to have American Special Operations forces join them in a supporting role, was taken by Defense Secretary Ashton B Carter. The White House, Cook said, was informed in advance.
Providing new details about the operation, American officials said on Thursday night that it had been mounted at the request of the Kurdish officials who insisted they had solid intelligence that the Islamic State was about to massacre prisoners, including a number of Pesh Merga fighters, as the Kurdish forces are known.
''They were going with or without us,'' a senior Defense Department official told The New York Times on the condition of anonymity to discuss a classified operation. ''We wanted to stand behind an important ally.''
Fears that the prisoners were in danger may have been reinforced by the militants' actions in recent days. An Iraqi in the Hawija area, who asked not to be named because he feared retribution from the Islamic State, said this week that the militants had recently executed 11 young men who were the sons or relatives of police officers or other Iraqi forces. He said their bodies had been displayed on a nearby bridge.
Five American helicopters were involved in the raid, a mix of Chinook and Black Hawk choppers. The American forces included commandos from the Delta Force counter-terrorism unit, officials said.
As the operation began, the United States conducted an airstrike to destroy a bridge near Hawija and hamper the Islamic State's ability to send reinforcements. But the operation soon became an intense firefight.
Kurdish forces were to take the lead in the operation while American soldiers, who were to play a supporting role, initially were near a wall that was some distance from the objective, officials said.