The Iraqi military said more than 30 rockets were fired at Camp Taji base.
This is the second attack this week on the base. On Wednesday, rockets killed two American troops and one British soldier there.
The US responded with air strikes targeting an Iranian-backed militia.
However, Iraqi officials say that Iraqi soldiers and policemen were killed in the strikes.
The Iraqi military says the latest attack on Taji must not be used by the US as a pretext for any action without Iraq’s approval.
Taji base, about 15km (nine miles) north of Baghdad, hosts foreign troops from the US-led coalition, whose mission is to train and advise Iraqi security forces.
Iraq’s Joint Operation Command said 33 Katyusha rockets were launched on the base. Seven rocket launchers and 24 unused rockets were later found nearby.
No-one has yet said they carried out the attack.
Wednesday’s deadly attack on the base prompted US strikes targeting five weapons storage facilities across the country, the US defence department said.