Two armed drones on Tuesday targeted Iraq's Ain al-Asad airbase, which hosts US forces and other international forces in western Iraq, two Iraqi military sources told Reuters.
It was the second attack against US forces in Iraq since early February when Iranian-backed groups in Iraq stopped their attacks against US troops.
In April, two drones were shot down near Ain al-Asad base, according to a US official.
No casualties have been reported, said the sources.
An Iraqi military official said defense systems downed one drone near the base perimeter.
Iraqi army patrols stepped up patrolling the areas around the base to prevent possible further attacks, said an Iraqi army official.
Attack comes right before Washington visit
The attack came less than a week before an expected visit by a high level Iraqi military delegation to Washington to continue talks on ending the US-led military coalition in the country.
Washington and Baghdad in January initiated talks to reassess the draw-down of the US-led coalition in Iraq, formed in 2014 to help fight Islamic State after the extremist Sunni Muslim militant group overran large parts of the country.
A US official, speaking on condition of anonymity, said a projectile appears to have targeted the base, but without causing casualties.