According to preliminary results on Kurdish outlet Rudaw, al-Sadr's coalition, Iraqi Prime Minister Haidar al-Abadi's Nasr (Victory) Coalition, and Hadi al-Amiri's Fatih (Conquest) Coalition are now believed to be in a three-way tie.
Current prime minister Haider al-Abadi, who is supported by the United States, trails both rivals but appeals to Iraqis to respect the final results.
An alliance spearheaded by nationalist cleric Moqtada Sadr looked on course Monday for a surprise triumph at Iraq's first nationwide election since the defeat of the Islamic State group.
A populist bloc organized by Sadr won the most seats in Iraq's parliamentary election, according to results from all 18 provinces released Monday.
His supporters celebrated in Baghdad. Transpiring from anti-government protests, which initially focused on addressing poor living conditions, the protest movement demanded reform of the political system, and is an important factor behind Sadr rally of support. Sadr has reinvented himself as an anti-graft crusader after rising to prominence as a powerful militia chief whose fighters battled United States forces after the 2003 invasion. "This shows to some extent that this election was an anti-establishment balloting, the results are a very clear indictment of the political elite". More than 10 million Iraqis voted.More news: Britain's ex-minister, campaigner Tessa Jowell dies of cancer
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Daesh first emerged in Syria and Iraq back in 2014, capturing swathes of land in both neighboring states.
The electoral surprise comes with tensions surging between the USA and Iran after Washington's withdrawal from the 2015 nuclear deal, sparking fears of a destabilising power struggle over Iraq.
Abadi was viewed as a frontrunner before the election. The family has long seen themselves as representing a rival Iraqi seat of Shia learning and influence to Tehran. He had no powerful political machine of his own when he took office.
As such, influential paramilitary commander, Hadi al-Amiri, who heads the Conquest (Fatah) list, fronted by the Badr Brigades and acts as the political arm of various Popular Mobilization Forces (PMF) militias as well as parties with traditionally close ties to Iran, still holds a key advantage. Sadr portrays himself as an Iraqi nationalist and is tired of Iranian support, thus he will be cautious of prompting a pro-Iranian figure.
The Victory Alliance of Prime Minister Haider al-Abadi, who has been backed by the global community, looked to have won in only one province.