The 62.5 voter turnout did not include ballots cast by security forces and others in early voting or the 275,000 Iraqis voting abroad.
'Maliki in the lead'
Hamdiyah al-Husseini, a senior official with IHEC, told reporters that turnout was particularly high in the country's autonomous northern Kurdish region, with 80 percent of voters in Dohuk casting ballots.
Informal tallies showed prime minister Nuri al-Maliki's State of Law coalition had polled well in Shia provinces while a secular, cross-sectarian bloc led by former premier Iyad Allawi appeared to be strong in Sunni areas of the north and west.
Sami al-Askari, a member of Maliki's coalition, said his coalition took about 45 per cent of the vote in Baghdad, the capital, and would win about half the seats in the Shia holy city of Najaf.
He said that it was running third in some northern areas behind Iraqiya and the Kurdish Alliance, he said.
"We will be the biggest bloc in the next parliament and according to the constitution we will be the bloc that will nominate the next prime minister," he said.
"But definitely we will need to ally with one or two other lists."
Mike Hanna, Al Jazeera's correspondent in Baghdad, said the first preliminary results would be based on just 30 per cent of the votes and may not be that representative of the actual vote.
"The prime intention is to get a governing bloc within the parliament which has 50 per cent plus one seat, which would then enable that particular bloc to form a government and nominate a prime minister," he said.
Thaer al-Naqeeb, an Iraqiya candidate and close aide to Allawi, said results were not clear so far but believed that Iraqiya got between 70-90 per cent of votes in the northern and western provinces.
Meanwhile the Supreme Islamic Iraqi Council (ISCI), which is one of the Shia parties grouped in the Iraqi National Alliance (INA), said the vote appeared evenly split between al-Maliki's bloc and INA in early counting.
Final results, certified by the supreme court after hearing appeals, were expected within about a month of the election.
More than 6,000 candidates from 86 political groups were competing for the 325 seats in parliament.
Despite tight security arrangements, the vote was marred by violence as a series of explosions left at least 38 people dead and 89 others wounded in the capital.
The bloodiest toll was from an explosion that destroyed a residential building in the Shaab district of northern Baghdad, killing 25 people and wounding at least eight more.