The United States has deployed 50 noncombat troops to an air base in Iraq's western province of Anbar.
The Pentagon said the military advisers were stationed at the Ain al-Asad air base, the largest in Anbar.
The mainly Sunni province is largely controlled by Islamic State (IS) fighters.
The deployment is the first reported time U.S. troops have been sent to Anbar since a U.S.-led coalition launched air strikes against IS targets in August.
U.S. forces left Iraq in 2011, but President Barack Obama last week announced plans to double the number of U.S. noncombat soldiers in Iraq to 3,000.
On November 9, Obama said the fight against IS was entering a "new phase" after four months of air strikes.