Moqtada al-Sadr was leading in Iraq's parliamentary election with more than half the votes counted, the electoral commission said, a surprise comeback for the powerful nationalist Shi'ite cleric who had been sidelined by Iran-backed rivals.
Shi'ite militia leader Hadi al-Amiri's bloc, which is backed by Tehran, was in second place, according to the count of more than 95 percent of the votes cast in 10 of Iraq's 18 provinces.
The preliminary results are a setback for Prime Minister Haider al-Abadi who, despite entering the election as the apparent frontrunner, appeared to be running third.
Sadr's apparent victory does not mean his bloc could necessarily form the next government as whoever wins the most seats must negotiate a coalition government, expected to be formed within 90 days of the official results.
Security and commission sources had earlier said Abadi was leading the election, which was held on Saturday and is the first since the defeat of Islamic State in the country.
Turnout was 44.52 percent with 92 percent of votes counted, the Independent High Electoral Commission said - that was significantly lower than in previous elections. Full results are due to be officially announced later on Monday.
Sadr and Amiri both came in first in four of the 10 provinces where votes were counted, but the cleric's bloc won significantly more votes in the capital, Baghdad, which has the highest number of seats.
The commission did not announce how many seats each bloc had gained and said it would do so after announcing the results from the remaining provinces.
A document provided to Reuters by a candidate in Baghdad that was also circulating among journalists and analysts showed results from all 18 provinces.
Reuters could not independently verify the document's authenticity but the results in it for the 10 provinces announced by the electoral commission matched those of the commission.
Reuters calculations based on the document showed Sadr had won the nationwide popular vote with more than 1.3 million votes and gained 54 of parliament's 329 seats. He was followed by Amiri with more than 1.2 million votes, translating into 47 seats, and Abadi with more than 1 million votes and 42 seats.