At least 10 rockets struck the Ain al-Asad base, located in western Anbar province, at 7:20 a.m., the source said. Coalition and Iraqi forces were investigating.
No deaths or injuries were immediately reported, according to Reuters.
The base was the same one targeted last February in an attack that left about 100 troops with head injuries. Patriot missiles were installed at the base after that attack.
Iraqi forces were leading the investigation into the latest attack, Col. Wayne Marotto, a U.S. military spokesman, tweeted.
The rocket fire came just days after sources told Fox News that the Combined Joint Task Force-Operation Inherent Resolve raised the threat level for U.S. troops serving in Iraq.
U.S. military officials were expecting possible retaliation after President Biden ordered an airstrike in Syria last week.
The U.S. strike was in response to rocket fire that targeted American presence in the region. That rocket fire killed a coalition contractor from the Philippines outside an airport in Irbil, in northern Iraq, the AP reported.
U.S. officials described the Biden-ordered response as “proportionate” to the preceding rocket fire.
The source of Tuesday’s rocket fire was not immediately known.
The rocket fire also came as Pope Francis planned a historic visit to Iraq for later this week that would make him the first pontiff to ever visit the country.
Fox News’ Jennifer Griffin and The Associated Press contributed to this report.