A cancellation would be the latest chapter of political turmoil in the war-scarred country which, almost four months after a general election, still hasn't chosen a new prime minister.

The vote for the head of state -- a post with a four-year mandate held by convention by a member of Iraq's Kurdish minority, and currently occupied by Barham Saleh -- was scheduled for noon (0900 GMT).

But there was little hope the 329-seat parliament in Baghdad's high-security Green Zone would be able to clinch the necessary two-thirds quorum to chose a new person for the largely ceremonial post.

The largest parliamentary bloc, led by powerful political kingmaker and Shiite Muslim cleric Moqtada Sadr and holding 73 seats, was first to announce a boycott, on Saturday.

It was followed on Sunday by the 51-member Sovereignty Coalition led by a Sadr ally, parliamentary Speaker Mohammed al-Halbussi.

The 31-seat Kurdistan Democratic Party (KDP) then announced it would also stay away, in order to "continue consultations and dialogue between political blocs".

Another key bloc, the Cooperation Framework grouping several Shiite parties, also said the session should not take place, citing the political turmoil since the October elections.

Those polls were marred by record-low turnout, post-election threats and violence, and a delay of several months until final results were confirmed.

Intense negotiations among political groups since then have failed to form a majority parliamentary coalition to name a new prime minister to succeed Mustafa al-Kadhemi.

- Corruption claims -

The process toward a presidential vote was further thrown into disarray on Sunday when Iraq's Supreme Court temporarily suspended Saleh's key challenger, Hoshyar Zebari, 68.

The court cited corruption charges against Zebari, a former foreign minister from the KDP -- allegations he denies.

"I have not been convicted in any court," Zebari had said in a television interview on Friday as the charges resurfaced alongside forecasts he would unseat Saleh.

Incumbent Saleh, the other frontrunner out of some 25 candidates, represents the KDP's main rival in Iraqi Kurdistan, the Patriotic Union of Kurdistan (PUK).

The Supreme Court said it was "temporarily" suspending Zebari after receiving a complaint from lawmakers that his candidacy was "unconstitutional" because of the graft claims.

The complainants cited his 2016 dismissal from the post of finance minister by parliament "over charges linked to financial and administrative corruption".

Public funds worth $1.8 million were allegedly diverted to pay for airline tickets for his personal security detail.

The complaint also cited at least two other judicial cases linked to him, including when he was Iraq's long-time foreign minister after the fall of dictator Saddam Hussein in the 2003 US-led invasion.

- 'Share the pie' -

A delay of Monday's presidential vote would deepen Iraq's political troubles since the October election.

Within 15 days after the new Iraqi president is elected, he must choose a prime minister from the largest block in parliament.

The prime minister, a Shiite Muslim according to political tradition, then has a month to form his government.

But while Sadr's bloc claims it can have enough seats for a "national majority government", the Coordination Framework has appealed to the Supreme Court to have their bloc recognised as the majority.

The country's apex court has rejected their demand, saying it could not decide now, as parliamentary blocs could change.

In Iraqi politics, said analyst Hamzeh Hadad, "everyone knows how to share the pie" but "no one knows how to be in the opposition".