About 40 soldiers were on the truck when the car bomber struck on Friday in Baquba, 60km northeast of Baghdad, the army said.
At least six others were wounded in the 8am (0400 GMT) blast in the town, army Colonel Abd Allah Shimmari said.
In a seperate incident one policeman was shot dead and three wounded when armed men opened fire on their patrol in western Baghdad on Friday, security officials and medics said.
Two civilians were also hurt in the shooting, al-Yarmuk hospital medics said.
Also on Friday, a roadside bomb hit a US military convoy in western Baghdad, police said.
One of the convoy's Humvees was damaged by the explosion in the Khadra area of the capital, and US forces closed the area, said police 1st Lieutenant Ali Hussain al-Hamadani.
No casualties were immediately reported and the US military said it could not confirm the attack.
On Thursday, at least 15 Iraqis were killed and up to 89 injured after two car bombs exploded in Baghdad, just hours after the assassination of an Iraqi brigadier-general and a police colonel, Aljazeera reported.
The attacks come amid a large US offensive on the western town of al-Qaim, near the Syrian border.
The US army claimed it had killed dozens of anti-US fighters. It also reported several US military personnel were killed and wounded in the offensive.
Aljazeera reports that the offensive has now entered its fifth day with fighting still raging in and around al-Qaim.