On Thursday morning a "suicide bomber wearing an explosive vest drove a booby-trapped car into a federal police checkpoint" near Hawija, north of Baghdad, one official said.

"Two policemen were killed and a third one wounded," in the attack, the official added.

Hawija is one of the last IS holdouts retaken by government troops a year ago and has long been a bastion of radical Sunni Muslim groups.

On Wednesday an IS suicide bomber blew a vehicle at a checkpoint on the outskirts of the Iraq border town of Al-Qaim, near the Syrian frontier, another of the last towns in Iraq to be recaptured from IS.

Also on Thursday, three members of Iraq's Hashed al-Shaabi paramilitary force, which played a key role in fighting IS, were wounded in a blast near Hawija, another security official said.

There was no immediate claim of responsibility for Thursday's attacks but IS said it was behind Wednesday's suicide bombing.

In a purported new audio message released last week, IS leader Abu Bakr al-Baghdadi called on his followers to "not give up the jihad against their enemy".

According to Hisham al-Hashemi, an expert on radical Islamist groups, about 2,000 IS jihadists are still active in Iraq, which declared victory over the jihadists in December last year.