Populist cleric Moqtada al-Sadr, a long-time adversary of the United States, has all but won Iraq's parliamentary election, the electoral commission has said.
The result would mark a surprise turn of fortune for the Shia leader.
In the first election since the so-called Islamic State group was defeated in the country, Iran-backed Shia militia chief Hadi al-Amiri's bloc was in second place, while Prime Minister Haider al-Abadi, once seen as the front-runner, trailed in third.
The preliminary results were based on a count of more than 91% of the votes cast in 16 of Iraq's 18 provinces.
Mr Sadr's bloc did not run in the remaining two provinces, Kurdish Dohuk and the ethnically-mixed oil province of Kirkuk.
The results there, which may be delayed due to tensions between local parties, will not affect his standing.
Unlike Mr Abadi, a rare ally of both the United States and Iran, Mr Sadr is an opponent of both countries, which have wielded influence in Iraq since a US-led invasion toppled Sunni dictator Saddam Hussein in 2003 and thrust the Shia majority into power.
Mr Sadr has led two uprisings against US forces in Iraq and is one of the few Shia leaders to distance himself from Iran.
Despite the election setback, Mr Abadi might still be granted a second term in office by parliament and he called on all political blocs to respect the results and suggested he was willing to work with Mr Sadr to form a government.
"We are ready to work and cooperate in forming the strongest government for Iraq, free of corruption," Mr Abadi said in a live televised address. Corruption has been at the top of Mr Sadr's agenda for several years.
Projecting himself as an Iraqi nationalist, Mr Sadr has a zealous following among the young, poor and dispossessed, but he had been sidelined by influential Iran-backed figures.
He cannot become prime minister as he did not run in the election, though his apparent victory puts him in a position to pick someone for the job.
But even then, his bloc might not necessarily form the next government. Whoever wins the most seats must negotiate a coalition government in order to have a majority in parliament.
The government should be formed within 90 days of the official results.
Saturday's election is the first since the defeat of IS last year. The group overran a third of Iraq in 2014.
Turnout was 44.52% with 92% of votes counted, the Independent High Electoral Commission said, the lowest participation rate in Iraq's post-Saddam history.
Full results are due to be officially announced later on Monday.
