BAGHDAD (AP) — Islamic State militants have ambushed a group of Iraq's Shiite-led paramilitary fighters, killing at least 27.

The Popular Mobilization Forces, an umbrella group of mostly Shiite militias, said on Monday that the attack took place the previous night in the al-Saadounya area, southwest of the northern city of Kirkuk, when the paramilitaries were conducting overnight raids.

The PMF says the attackers were disguised in army uniforms. It says clashes lasted for at least two hours and that some of the militants were killed while others fled the area.

Brig. Gen. Yahya Rasool, a spokesman for Iraqi military, blamed IS "sleeper cells" and said Iraqi forces were searching the area to find the perpetrators.

IS claimed responsibility for the attack in a statement on its Aamaq news agency.