A statement from the US Central Command, which oversees military activities in Central Asia, the Middle East and North Africa, did not identify the victim. It said further details would be forthcoming.
US casualties in Iraq dropped to near zero after most American troops were withdrawn in 2011, but rose again to 17 last year, and seven so far this year with the latest death, according to the iCasualties.Org website, which tracks coalition deaths and injuries.
The United Nations estimates that more than half a million civilians have fled Mosul since the offensive on the country's second city began.
The jihadists are expected to make a bloody last stand in Mosul's Old City, where an estimated 4,00,000 civilians remain trapped.