Police officials say two carloads of gunmen attacked the checkpoint in the city of Fallujah early today and started firing.
Fallujah, a former Al Qaeda stronghold, is 65 kilometers (40 miles) west of Baghdad.
A medic in a nearby hospital confirmed the casualties. All officials spoke on condition of anonymity because they are not authorized to talk to media.
Iraqi security forces are struggling to contain the country's most relentless round of violence since the 2011 US military withdrawal. Insurgents frequently attack the army and police in an attempt to undermine the Shiite-led government.