Gunmen killed three Iraqi policemen during an attack on a guard post near the city of Kirkuk late on Monday, officials said.
Another federal police officer was wounded in the assault in the town of Altun Kupri, on the boundary between the northern provinces of Kirkuk and Erbil, the interior ministry added.
There was no immediate claim of responsibility but ISIS militants are active in the area and a security source said it was likely they were involved.
Iraq declared victory over the group, which once held large swathes of the country, in December 2017.
But ISIS has switched to hit-and-run attacks aimed at undermining the Baghdad government.
Its fighters have regrouped in the Hamrin mountain range in the northeast, which extends from Diyala province, on the border with Iran, crossing northern Salahuddin province and southern Kirkuk.
Security forces killed eight militants in the western Anbar province, the military said in a statement late on Monday.