The attack happened late on Saturday as the men were passing between the towns of Latifiya and Yusufiya, about 35km south-west of Baghdad.
"They were returning from a training course in Amman," a police spokesman said. "No one survived and the attackers escaped."
Iraqi insurgents regularly attack military convoys and vehicles carrying foreign contractors on the main road which leads south from Baghdad towards the city of Karbala.
US forces recently launched an operation in the region
surrounding Latifiya and Yusufiya to try to weed out fighters carrying out attacks there.
Hundreds of Iraqi police and recruits have been killed in car bomb attacks, drive-by shootings and ambushes over the past year, as anti-US fighters try to disrupt US attempts to establish a stand-alone Iraqi security force.