The attack happened today in Ramadi, the provincial capital of Anbar province, where Iraqi security forces have been battling militants who took control of parts of the town in late December.
Police say militants stole the Humvee and painted it with military colours to trick soldiers into letting it by.
Elsewhere today, police say a roadside bomb targeting a military vehicle in Baqouba, 60 kilometres northeast of Baghdad, killed a captain and wounded four soldiers.