The U.S.-backed Syrian Democratic Forces, which control swathes of northeast Syria, referred questions to the U.S.-led coalition under which American troops are deployed in the zone.
In March, 25 U.S. troops were wounded in strikes and counter-strikes in Syria, which also killed one U.S. contractor and injured another.
U.S. forces first deployed into Syria during the Obama administration's campaign against Islamic State, partnering with a Kurdish-led group called the Syrian Democratic Forces.
Thousands of other Islamic State fighters are in detention facilities guarded by Kurdish-led Syrian Democratic Forces, America's key ally in the country.
U.S. officials say that Islamic State could still regenerate into a major threat.
Persons:
Obama, Bashar al, Assad
Organizations:
U.S, military's, Command, U.S . Central Command, Syrian Democratic Forces, Islamic State, Islamic
Locations:
Syria, U.S, Kurdish, Damascus, Islamic State, Iran, State, Iraq, Russia, Iranian