Iraqi national armed forces, aided by militia groups and advised by US forces, have been engaged in the battle to retake Mosul since October 2016. Daesh took control of the city in 2014.
The command provided no details beyond the information that the soldier had died in an "explosive device blast," but promised to release more information as appropriate, according to CBS News.
It is likely that the serviceman died after a blast from an improvised explosive device (IED) left by Daesh militants. US troops are not supposed to be taking part in actual combat in the city, but providing advance support and advice and helping with de-mining efforts around the area.
Daesh is known to rig buildings, cars and even toys and items of food and drink with explosives as it retreats, according to media reports.
The coalition commanders were forced to temporarily pause the offensive last month after the civilian population of Mosul suffered "catastrophic" casualties, caused mainly by artillery and airstrikes by coalition forces.
This is the second US military casualty in the battle for Mosul and the fifth US combat death in Iraq since launching operations against Daesh in 2014.