A rocket attack on Thursday night slammed into an Iraqi base in the remote province of Kirkuk where American troops are stationed, Iraqi and US security sources told AFP.
There were no immediate reports of casualties.
It was the first attack on the K1 base since December 27, when a volley of around 30 rockets killed a US contractor there, which Washington blamed on Kataeb Hezbollah, a hardline Iraqi military faction close to Iran.
The US then carried out retaliatory strikes that left 25 Kataeb Hezbollah fighters dead and, days later, killed Iran's pointman on Iraqi affairs Qasem Soleimani.