The 73-member bloc's parliamentary chief, Hassan al-Izari, told a news conference they will not attend Monday's session in the 329-seat house, making a vote unlikely although technically a quorum could be reached.

The vote for president, a largely ceremonial role traditionally reserved for Iraq's Kurds in post-Saddam Iraq, primarily pits the incumbent Barham Saleh against his top challenger, former minister Hoshyar Zebari, candidate of the Kurdistan Democratic Party (KDP).

The latter's candidacy has stirred controversy due to years-old corruption accusations against him in court that led to his 2016 dismissal from the post of finance minister.

"Our withdrawal is a message to the Kurds, in particular to the KDP, for them to agree on a single candidate," a Sadrist MP told AFP, speaking on condition of anonymity due to the sensitivity of the issue.

The MP, whose bloc's triumph in general elections last year has left Sadr in the driving seat in complex negotiations to select a new prime minister, said Zebari was "not a consensus (candidate)".

After having served for a decade as foreign minister followed by two years as finance minister, parliament fired Zebari in September 2016, notably over charges that $1.8 million of public funds were diverted to pay for airline tickets for his personal security detail.

Zebari has always denied any corruption accusations.

"I have not been convicted in any court," he said in a television interview on Friday night as the charges resurfaced alongside forecasts he would unseat Saleh, candidate of KDP's rival in Iraqi Kurdistan, the Patriotic Union of Kurdistan (PUK).