Troops board a plane at Spangdahlem Air Base, Germany, on April 7, 2016, on their way to participate in Operation Inherent Resolve.
In May, a U.S. service member died in Syria after being injured in a vehicle roll-over.
Two U.S. service members were killed during combat operations in northern Iraq on the morning of August 13, a spokesman for Operation Inherent Resolve announced in a statement.
"Initial reports indicate the incident was not due to enemy contact", the statement continued, adding the circumstances are "under investigation". It did not identify the soldiers.
More than 5,000 US troops are taking part in the war against IS in Iraq, according the Pentagon.
"The fallen service members were fighting to defeat a truly evil enemy and to protect our homeland", the statement quoted Lt. Gen. Stephen Townsend, the commander of USA forces battling the Islamic State (IS) group in Iraq as saying. "There are no words to describe the respect I have for you and sorrow I have for your loss".
After a nine-month battle to oust ISIS from its last urban stronghold in Mosul, Iraqi forces - closely supported by the USA -led coalition - are preparing to retake the ISIS-held town of Tal Afar west of the city.