"Two U.S. service members were killed and five injured conducting combat operations in northern Iraq, Aug. 13, 2017", the U.S. Central Command said in a statement posted on its website.
A separate statement released by the Islamic State on Sunday, apparently referring to the same incident, said it had carried out a rocket attack on US positions east of the Iraqi city of Tal Afar that the group claimed killed four American soldiers and injured six.
Five other American service members were hurt from Sunday's incident.
It added that an investigation was under way, but gave no further details about what happened or where.
More than 5,000 USA troops are partaking in the war against IS in Iraq, agreeing the Pentagon.
The slain troops were part of the so-called US-led coalition, which was formed in 2014, with a purported aim of fighting the Takfiri Daesh terrorist group in Iraq but it was later expanded to include territories in eastern and northern Syria.
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.
But the Islamic State retains control of several towns in both countries that are populated by tens of thousands of civilians, and their safety has become a growing concern as the military campaign - especially coalition airstrikes - have intensified.
Iraq's PM proclaimed triumph against IS in Mosul in July, and Iraqi powers are presently get ready to retake the IS-held town of Tel Afar, toward the west.