Islamic State fighters have killed a member of the US armed forces in northern Iraq, when they pushed through a forward line of Iraqi Kurdish forces, officials said.
He is the third American killed in direct combat since a US-led coalition launched a campaign against the jihadist group in 2014.
"It is a combat death, of course, and a very sad loss. I don't know all the circumstances of it," US Defense Secretary Ash Carter told reporters during a trip to Germany,
US military official said the US-led coalition helped the Peshmerga repel an attack by providing air support from F-15 jets and drones.
The official, speaking on condition of anonymity, said the man was killed "by direct fire" from Islamic State.
Carter's spokesman, Peter Cook, said the incident took place during an Islamic State attack on a Peshmerga position some 3-5km behind the Iraqi Kurdish fighters' forward line.
In mid-April the United States announced plans to send an additional 200 troops to Iraq, and put them closer to the front lines of battle to advise Iraqi forces in the war against Islamic State.
Last month, an Islamic State attack on a US base killed Marine Staff Sergeant Louis Cardin and wounded eight other Americans providing force protection fire to Iraqi army troops.
The Islamist militants have been broadly retreating since December, when the Iraqi army recaptured Ramadi, the largest city in the western region.
Last month, the Iraqi army took the nearby region of Hit, pushing them further north along the Euphrates valley.
But US officials acknowledge that military gains against Islamic state are not enough.
Iraq is beset by political infighting, corruption, a growing fiscal crisis and the Shi'ite Muslim-led government's fitful efforts to reconcile with aggrieved minority Sunnis, the bedrock of Islamic State support.
