An alliance headed by nationalist cleric Moqtada Sadr and a rival bloc of pro-Iranian former fighters appeared to surge Monday in surprise preliminary results from Iraq's first poll since the defeat of the Daesh group.

If confirmed, the outcome would throw open the race to become the next prime minister, as internationally favored incumbent Haider al-Abadi lagged behind after a vote hit by record abstentions.

According to partial results seen by AFP, the Marching Towards Reform alliance of Shiite cleric Sadr and his communist allies was ahead in six of Iraq's 18 provinces and second in four others.

Sadr has reinvented himself as an anti-graft crusader after rising to prominence as a powerful militia chief whose fighters battled U.S. forces after the 2003 invasion.

While long railing against the United States, the nationalist firebrand has also distanced himself from its key rival Iran, drawing closer to regional Sunni powerhouse Saudi Arabia.

Next in the running is the Conquest Alliance (Al-Fatah), made up of ex-fighters from mainly Iran-backed Hashd al-Shaabi paramilitary units that battled Daesh, with results putting them ahead in four provinces and second in eight others.

The head of the list is Hadi al-Amiri, a long-time ally of Tehran, whose forces ended up battling alongside the U.S. to oust the terrorists.

Speaking to Anadolu Agency on Monday, a leader of the Al-Fatah coalition said it snatched 11 seats in the capital Baghdad and 6 seats in Basra. The coalition also won 3 seats in Babel and two in each of Karbala, Najaf, Dhi Qar, Wasit, al-Muthanna, al-Diwaniyah and Diyala and one seat in Nineveh and Anbar, the leader said on condition of anonymity because he was unauthorized to speak to media.

The Hashd al-Shaabi is a largely Shiite fighting force that has been instrumental in Iraq's fight against the Daesh terrorist group. The force was incorporated into the Iraqi army in 2016.

Many of the candidates on Fatah were militia commanders before they cut their official ties with the force in order to seek office.

Fatah's strong result will be seen as a victory for Iran as it seeks to protect its interests in the Iraq, including the militias it finances and has sometimes directed to fight alongside its forces in Syria. Al-Sadr is a staunch foe of Iranian and American influence in Iraqi politics.

Both Sadr and Amiri are long-time political veterans well-known to Iraqis, but they pitched themselves as seeking to sweep clean the country's reviled elite.

The complex electoral arithmetic of the Iraqi system, however, means that the final makeup of 329-seat parliament is still far from decided.

The ballots of some 700,000 security personnel who voted and Iraqis abroad were yet to be tallied up, meaning Abadi could get a boost five months after he announced victory over Daesh.

Whatever the outcome, there looks set to be lengthy horse-trading between the main political forces before any new premier and a coalition government can be installed.

Sadr, who did not stand as a candidate and therefore cannot become premier, appears in pole position to play kingmaker after years on the sidelines.

The electoral surprise comes with tensions surging between the United States and Iran after Washington's withdrawal from the 2015 nuclear deal, sparking fears of a destabilizing power struggle over Iraq.

Abadi, who came to power as Daesh swept across Iraq in 2014, has been a consensus figure who balanced off the United States and Iran.

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

Al-Abadi sought to retain his post as prime minister bu faced stiff competition from his predecessor, Nouri al-Maliki, as well as al-Sadr and the Fatah.

Any political party or alliance must gain a majority of Iraq's 329 seats in parliament to be able to choose a prime minister and form a government. Dozens of alliances ran for office in these elections and months of negotiations are expected before any one alliance can pull together the 165 required seats.

Until a new prime minister is chosen, al-Abadi will remain in office, retaining all his power.

U.S. Secretary of State Mike Pompeo, whose country still has troops in Iraq from the fight with Daesh, on Saturday lauded the poll and called for an "inclusive government, responsive to the needs of all Iraqis".

But the ballot saw a record low turnout, as only 44.5 percent of eligible voters headed to the polls in the lowest participation rate since the 2003 U.S.-led ouster of Saddam Hussein.

According to the election commission, around 10.8 million Iraqis out of 24 million eligible voters took part in the vote.

The announcement included full returns from only 10 of the country's 19 provinces, including the provinces of Baghdad and Basra.

After the announcement that the Marching Towards Reform was ahead in Baghdad, supporters took to the streets in the capital to celebrate early Monday.

The center of the celebrations is Sadr City, an impoverished quarter that is home to some 3 million people and is named after the cleric's late father, Ayatollah Mohammad Sadq al-Sadr.

Crowds of mainly young people waved flags and pictures of the populist nationalist cleric Sadr while fireworks fired off into the night sky.

Zeid al-Zamili, 33, described the vote as a "new chapter for the Iraqi people".

"We're done with corruption and the corrupt, we've suffered for years, now everything will change," added another supporter in a black t-shirt.

Whoever emerges as premier will face the mammoth task of rebuilding a country left shattered by the battle against Daesh -- with donors already pledging $30 billion (25 billion euros).

Over two million people remain internally displaced across the country and Daesh - while weakened -- still has the capability to launch deadly attacks.

Political power in Iraq is traditionally divided along sectarian lines among the offices of prime minister, president and parliament speaker. Since the first elections following the 2003 U.S.-led toppling of Saddam Hussein, the Shiite majority has held the position of prime minister, while the Kurds have held the presidency and the Sunnis have held the post of parliament speaker.

The constitution sets a quota for female representation, stating that no less than one-fourth of parliament members must be women. Nearly 2,600 women are running for office this year.