According to partial official results obtained by AFP, the Marching Towards Reform alliance of Shiite cleric Moqtada Sadr and communists was ahead in six of Iraq's 18 provinces and second in four others.

The Conquest Alliance, made up of ex-fighters from mainly Iran-backed paramilitary units that battled the Islamic State group, was ahead in four provinces and second in eight others.

The Victory Alliance of Prime Minister Haider al-Abadi, who has been backed by the international community, looked to have won in only one province.

If the surprise results are confirmed then it would throw open the race for Iraq's new premier, following the first elections after the defeat of IS.

The complex electoral arithmetic of the Iraqi system means that the final makeup of the parliament is still far from decided.

Several senior political figures had previously told AFP that preliminary results put Abadi in the lead, on course to scoop 60 of the 329 parliament seats up for grabs.

Abadi -- who came to power as IS swept across Iraq in 2014 -- is a consensus figure who has balanced off the United States and Iran.

The other leading challengers have often taken a stronger stance against the United States.

Whatever the outcome, there looks set to be lengthy horse-trading between the main political forces before any government can be formed.

The ballot Saturday was hit by record abstentions, with only 44.5 percent of eligible voters heading to the polls in the lowest turnout since the 2003 US-led ouster of Saddam Hussein.