Multiple rockets were launched at Iraq's Ain al-Asad airbase which houses US-led forces late on Thursday, US and Iraqi sources said, according to the Reuters news agency.
No damage or casualties were reported. Two US officials said the base itself had not been struck in the attack.
The attack came two days after a military summit in Washington where Iraqi and US officials discussed winding down the coalition's work a decade after it was formed to fight Islamic State (ISIS) as it stormed across Iraq and Syria.
The Ain al-Asad base came under attack by two armed drones last week, but that attack was the first one against US forces in Iraq since early February, when Iranian-backed groups in Iraq announced they would stop their attacks against US troops.
That announcement came two days after a drone attack in Jordan killed three US service members and wounded dozens of others.
Before stopping their attacks in February, the pro-Iranian militias in Iraq had upped the volume of their attacks, and launched dozens of attacks on bases in Iraq and Syria which host US troops.
The US retaliated by striking Iranian-linked sites in both Iraq and Syria.