At least two people have been killed and six injured when multiple ISIL suicide bombers attacked a base in northern Iraq, security sources said.

Two of the attackers died overnight when they detonated their vests at the entrance to the K1 base, where US advisers are also stationed.

Three more were killed by Kurdish Peshmerga forces who control the Kirkuk area where it is situated.

"They were wearing uniforms like the Kurdish Peshmerga and had shaved their beards to look like us," one officer told Reuters news agency.

The Islamic State of Iraq and the Levant (ISIL, also known as ISIS) claimed responsibility for the attack in a statement, saying it had killed and wounded dozens of "crusaders and apostates", referring to the Peshmerga and Western military advisers.

Iraqi forces backed by a US-led coalition are fighting to dislodge ISIL from Mosul, 140km northwest of Kirkuk, but large pockets of territory remain under the group's control, including Hawija, which is near the targeted base.

In recent months, ISIL has stepped up its attacks in different parts of Iraq in an effort to distract attention from the ongoing US-backed campaign to remove it from Mosul in northern Iraq.

Mosul offensive

On February 19, Iraqi forces started a major offensive to wrest back the western section of Mosul from ISIL, almost a month after they recaptured the eastern part of the city.

The western side of Mosul is thought to be the most difficult to retake in the ongoing campaign because of the high population density there.

ISIL seized Mosul, Iraq's second-largest city, in a blitz in mid-2014.

As hundreds of thousands of civilians are still in Mosul, anti-ISIL forces have had to limit their use of aerial attacks and artillery in the city. Nevertheless, hundreds of civilians have been killed by coalition air raids and shelling, as well as in the counter-attacks launched by ISIL.

The US-led coalition bombing ISIL positions in Iraq admitted that it carried out air raids in March at a location in west Mosul where officials and residents say scores of civilians were killed.

READ MORE: Mosul civilians - 'Who knows who was shooting?'

Hundreds of thousands of civilians have been forced to flee their homes in Mosul as the military offensive to re-take the city rages on.

ISIL is now besieged in the northwestern corner of Mosul, which includes the historic Old City centre and the medieval Grand al-Nuri Mosque and its landmark leaning minaret.

The mosque is a hugely symbolic prize as it is where ISIL leader Abu Bakr al-Baghdadi made a rare public appearance in July 2014 and declared the group's self-styled caliphate, after the armed group seized almost one third of Iraq.

According to Iraq's authorities, ISIL now controls less than seven percent of Iraq.