Servicemen in uniform queued up to cast their ballots two days before the rest of the country heads to the polls for a parliamentary election Saturday, just five months after the months-long battle against the jihadists drew to a close.

Iraqis are hoping that the vote can lock in the fragile peace that has settled over their country some 15 blood-soaked years since the US-led ouster of dictator Saddam Hussein.

But they face the mammoth task of rebuilding after years of devastating conflict, while IS continues to pose a major security threat.

Police and presidential guard members waited on Thursday morning outside a school in central Baghdad that had been turned into a polling station.

Security was tight after IS threats, and voters were frisked several times as they entered to cast their ballots.

Police special forces officer Ahmed Qassem told AFP that he voted for the candidate who "will help the poor and fight corruption".

"The most important thing is that it is the people who are choosing their representatives and who will become prime minister," the 38-year-old said.

In the southern city of Basra, police and soldiers filed out of polling stations with indelible ink on their fingers to show they had voted.

Traffic policeman Hassan Mohammed said he wanted "change" and hoped for a "new government that will bring us a better future".

To the north in the autonomous Kurdish enclave, fighters in the region's peshmerga security forces -- which played a key role in fighting IS -- also lined up to vote.

Prime Minister Haider al-Abadi is angling for a new term as he takes credit for the fightback against the jihadists and for seeing off a Kurdish push for independence.

But stiff competition from within his Shiite community, the majority group which dominates Iraqi politics, is likely to fragment the vote and spell lengthy horse-trading before any government is formed.

Overall, some 24.5 million voters are registered for the elections, with some of roughly one million Iraqis living abroad also set to begin voting Thursday.