Lebanon's Saad al-Hariri said on Wednesday he was not a candidate to be prime minister of a new government, leaving no obvious alternative to head a cabinet that must tackle the worst economic crisis since the 1975-90 civil war.

Hariri, the outgoing prime minister and Lebanon's leading Sunni politician, made the statement on the eve of formal consultations to designate the new prime minister, a post reserved for a Sunni in Lebanon's sectarian system.

"I announce that I will not be a candidate to form the coming government," Hariri said in a statement.

"I am heading tomorrow to take part in the consultations ... on this basis, insisting that they not be delayed for any reason," he said.

Hariri did not say who he would nominate for the post in the consultations which President Michel Aoun is due to host on Thursday. Aoun, a Maronite Christian, is required to designate the candidate with the most support among Lebanon's 128 MPs.

The only candidate with the support of Lebanon's Sunni Muslim religious establishment, Hariri had appeared the only candidate for the job earlier this week despite political tension with adversaries including Aoun.

But the picture was complicated when the Christian Lebanese Forces said it would name neither Hariri nor anyone else in the consultations, meaning his candidacy would not enjoy the support of either of Lebanon's two main Christian parties.

Hariri resigned as prime minister on Oct. 29, prompted by protests against a political elite accused of overseeing rampant state corruption.