A rocket slammed into an Iraqi base where American troops are stationed in the remote province of Kirkuk, Iraq's military and a US security source told AFP on Thursday night.
It was the latest in a string of nearly 20 rocket attacks since late October on US troops stationed across the country as well as on the American embassy in Baghdad.
According to three separate Iraqi security sources, the Katyusha rocket hit an open area on the K1 base at around 8:45pm local time (1745 GMT).
Both US troops and Iraqi federal police forces are stationed there but neither sustained casualties, according to a statement from Iraq's military.
It said security forces found the launch pad from which the rocket was fired, with 11 more rockets still inside, but the perpetrators were on the run.
An Iraqi security source told AFP that the launch pad was found about five kilometres (three miles) from the base, in a multi-ethnic area.
It was the first attack on K1 since December 27, when a volley of around 30 rockets killed a US contractor there and unleashed a dramatic escalation.
Washington blamed the rockets on Kataeb Hezbollah, a hardline Iraqi military faction close to Iran, and conducted retaliatory strikes that killed 25 of the group's fighters.
Supporters of the group then surrounded the US embassy in Baghdad, breaking through its outer perimeter in an unprecedented breach.
Days later, a US drone strike at Baghdad airport killed Iran's pointman on Iraqi affairs Qasem Soleimani and his right-hand man, Kataeb Hezbollah co-founder Abu Mahdi al-Muhandis.
In outrage, Iraq's parliament voted to oust all foreign forces from the country, including around 5,200 US troops deployed to help local forces beat back remnants of the Islamic State group.
Iran carried out in own strikes in response to Soleimani's killing, firing a barrage of ballistic missiles at the sprawling Ain al-Asad base in western Iraq on January 8.
The troops had prior warning and none were killed, but more than 100 have since been diagnosed with traumatic brain injuries.