The US Department of Defense said Sunday that 1st Lt. David Bauders, 25, died on Friday at the Al Asad Air Base in western Iraq's Anbar Province. He was part of the Washington National Guard's 176th Engineer Company.
The Pentagon said that the circumstances of Bauders' death remain unclear and are under investigation.
While the US has combat troops in Iraq the majority of its forces are there as advisors to train Iraqi and Kurdish forces in the fight against the Islamic State group (ISIS).
Last Tuesday, a US Navy SEAL named Charles Keating was killed fighting off a surprise ISIS attack on Peshmerga positions in the town of Tel Skof north of Mosul.
To date the US has suffered three combat casualties since returning to Iraq to fight ISIS.
Staff Sgt. Louis F. Cardin, 27, was killed in March by ISIS rocket fire against a Marine Corps artillery base in Makhmour, some 60 kilometers southwest of Erbil.
The first American casualty was back in October when Master Sgt. Joshua L. Wheeler, 39, was killed rescuing 70 ISIS captives in Hawija in a joint US-Peshmerga special forces raid.
