Three rockets landed on a military base hosting U.S. forces north of Baghdad late on Monday, an Iraqi military statement said, without providing further details.
A military source earlier said two mortar shells had landed in the Iraqi section of the sprawling Taji base, located about 30 km (18 miles) north of the Iraqi capital, and another outside it.
No casualties were caused by the shelling, the source said. He said sirens wailed in the U.S. section of the base during the incident.
There was no immediate claim of responsibility for the attack.
It came amid heightened tension in the region between the United States and Iran that has also played out on Iraqi territory.
U.S. officials said last month there was an increased threat from Iran-backed militias against U.S. interests in Iraq, and the U.S. embassy in Baghdad evacuated hundreds of staff.
Washington and Tehran have both said they do not want conflict, but analysts warn that incidents including by what they call "rogue elements" within Iran-backed armed groups could lead to a wider escalation.
Islamic State is also active in areas around Taji and in northern and western Iraq and has carried out dozens of attacks on security forces in recent months.
Want to enjoy 'Zen' reading - with no ads and just the article? Subscribe todaySubscribe now