Charlie Keating IV is the third American serviceman to die in combat in Iraq since the USA -led coalition launched its campaign against the Islamic State in the summer of 2014, according to military officials.
The small team of advisers went to Teleskof, about 14 miles north of Mosul, to meet with Kurdish peshmerga forces.
Keating was an adviser to the Kurdish Peshmerga troops and part of a quick reaction force that was trying to rescue the American troops during the attack.
The Obama administration says the death of a third US service member since the military stepped-up its fight against the Islamic state group in Iraq is not a sign that USA troops are becoming actively involved in the fight. He'd also been to Afghanistan once.
Earnest continued, saying, "Secretary (Ash) Carter, earlier today has described his death as a combat death".
"Our state and nation are in mourning today over the loss of a USA serviceman - and one of America's finest", Arizona Gov. Doug Ducey said in a statement.
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General Wahid Kovali, the leader of a Peshmerga counter-terrorism unit that fought alongside the U.S. forces, told The Guardian that Keating and the QRF "were very good fighters".
Two US military personnel have already been killed by ISIL in Iraq: an American Marine by rocket fire in March and a special forces soldier who died of wounds received during a raid on a prison last October.
Warren maintained that the primary role of USA troops in Syria would be to advise and assist, but the events on Tuesday that left Keating and several Peshmerga soldiers dead shows just how quickly these missions can turn into full on combat.
Keating was hit Tuesday morning and evacuated for medical treatment, but "his wound was not survivable", Warren said.
"Our deepest heartfelt condolences go out to that American service member and his family", Warren said. The U.S. has been training, equipping and advising Pershmerga forces as well as Iraqi security forces, and the Pentagon recently pledged up to $415 million in aid to the Kurds. Keating and elements of his team were responding to a local Peshmerga force's request for support during when they were attacked.
Keating IV, 31, of San Diego, California, died May 3 in Tall Usquf, Iraq, of combat related causes.
"He was my number one runner all four years, but he was always there cheering on and pushing the other runners", said Rob Reniewicki, Keating's former track coach at Arcadia High School in Phoenix.