Iraqi Shiite cleric and leader Moqtada al-Sadr was once wanted by the US

A radical cleric who led militia into bloody battles with coalition forces in Iraq is on course to win the country's election.

Firebrand Iraqi Moqtada al-Sadr formed the Mahdi Army in 2003 which was responsible for bloodshed on the streets of Basra and the shooting down of coalition planes.

Four British airmen were killed in Basra in May 2006 when a helicopter was shot down. The Shia militia announced it would kill any British troops it saw.

Al-Sadr’s forces offered rewards for the capture and killing of British soldiers and he was implicated in multiple kidnappings.

The militia also hunted US troops in Najaf, just south of Baghdad. At least 70 US deaths are attributed to his forces in Najaf alone.

Now, he has reinvented himself and has formed a political coalition with communists.

It is a surprise comeback for the powerful nationalist Shi'ite cleric who had been sidelined by Iran-backed rivals.

The Marching Towards Reform alliance was ahead in six of Iraq's 18 provinces and second in four others, early results show.

The alliance is beating Prime Minister Haider al-Abadi, who has been backed by the international community. The Prime Minister is ahead in just one province, AFP figures showed.

Sadr will not become prime minister as he did not run in the election but his apparent victory puts him in a position to pick someone for the job. Winning the largest number of seats does not automatically guarantee that, however. The other winning blocs would have to agree on the nomination.

Followers of Shiite cleric Muqtada al-Sadr, seen in the posters, celebrate after the preliminary results of the parliamentary elections are announced, in Tahrir Square, Baghdad

Sadr, once the voice of the opposition to the war in Iraq, faces competition from another alliance.

Shi'ite militia leader Hadi al-Amiri's Conquest Alliance, 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.

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.

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.