The May 12 poll delivered a shock win for populist cleric Moqtada Sadr, who faces a huge task to form a governing coalition despite winning the most seats in parliament.

But with the results yet to be ratified by Iraq's Supreme Court, a government official told parliament on Thursday that intelligence services had conducted tests which showed it was possible to hack voting machines and manipulate the results.

The cabinet decided to form a commission "to study reports and information on the electoral process" and make recommendations, Prime Minister Haider al-Abadi said in a televised address.

Experts said the probe could lead to anything from local recounts to the entire vote being annulled.

Multiple candidates and parties are expected to appeal the results of Iraq's first poll since the defeat of the Islamic State group.

Limited recounts have already been ordered in the flashpoint multi-ethnic province of Kirkuk, where clashes between communities prompted authorities to impose an overnight curfew.

The International Crisis Group said Thursday it was "deeply concerned" about the possibility of further inter-ethnic violence there and called for a recount "to restore confidence in the institutions vital to manage deeper divisions over the contested, oil-rich area".