The attack, which occurred about 7:30 am local time (1000 IST) 60 kilometres (37 miles) south of the northern city of Mosul, also wounded another two police.
The morning assault was followed by a roadside bomb exploding as emergency personnel travelled to the scene, wounding two more people.
In a separate incident, gunmen shot dead a man in Baquba, a city north of Baghdad.
The attacks came a day after 29 people were killed in violence in Iraq.
More than 2,900 people have died in attacks so far this year, according to AFP figures based on security and medical sources.
Iraq has faced years of attacks by militants, but analysts say widespread discontent among members of its Sunni Arab minority that the government has failed to address has fuelled the surge in unrest this year.