Two rockets targeted a US patrol base in northeastern Syria late Friday, the third such attack in nine days, US Central Command said.
Centcom did not indicate who fired the rockets but said, in a statement, that they aimed at "coalition forces at the US patrol base in Al-Shaddadi, Syria".
Hundreds of American troops are still in Syria as part of the fight against IS remnants.
Turkey says it is targeting rear bases of the Kurdistan Workers' Party (PKK), designated as a terrorist group by the European Union and the United States, and the Syrian Kurdish People's Protection Units (YPG), which dominate the SDF.
Both Kurdish groups denied responsibility for the Istanbul attack.