At least 25 people were killed and 18 injured in Thursday's bomb attack on funerals for Iraqi fighters killed by militants, according to a new toll from pokillice and medics.

“Two bombs exploded as the funeral procession was entering the cemetery” in Asdira, village mayor Salaheddin Shaalan told AFP.

The Sunni village is south of Sharqat, one of the last bastions of the Islamic State group in the country's north to be retaken by Iraqi forces.

“In total, 25 people were killed and 18 injured, four of whom are still in critical condition,” a police officer told AFP on Friday, on condition of anonymity, revising an earlier death toll.

Medical sources confirmed the new figures.

It was the deadliest attack in Iraq since a January 16 double suicide bombing in Baghdad claimed 31 lives.

Thursday's attack took place during a funeral for five members of the Hashed al-Shaabi paramilitary units killed Wednesday night in the same village, 250 kilometres (150 miles) north of Baghdad.

The mostly Shiite paramilitary units, which also include Sunni tribal forces, played a key role alongside the army in expelling militants from Iraqi towns last year.

The Iraqi government declared victory over IS in December after pushing IS militants out of their final holdouts along the border with Syria.

But the group retains the capacity to strike despite losing control of vast swathes of Iraqi territory it seized in 2014.

It still clings to pockets of desert in war-torn Syria and appears to be able to cross the porous border between the two neighbours.

Militants sometimes manage to snatch control of roads at night, especially in the Salaheddin province where Thursday's attack took place, and Anbar province along the border with Syria, security experts say.

Iraq is gearing up for legislative elections set for May 12.

Since the 2003 US-led invasion and the fall of Saddam Hussein's regime, polls in Iraq have consistently been marred by violence.

But in the run-up to next month's elections, the country has enjoyed a respite from violence.