"The consultations will start Monday at noon," Parliament Speaker Nabih Berri told reporters after meeting President Michel Suleiman.

Suleiman asked Hariri to stay on as caretaker prime minister on Thursday after 11 ministers quit in a dispute over an investigation into the 2005 assassination of Hariri's father.

According to the constitution, Lebanon's president nominates a prime minister to form a new government after consultations with members of Parliament.

It was not clear how long consultations will take.

Officials have declined to say whether Hariri, whose coalition won a 2009 parliamentary election, will be asked to form a new government, or if someone else would be nominated.

Boutros Harb, a parliamentarian close to Hariri, said: "I do not see a government in the country without Saad Hariri."

Hariri was meeting US President Barack Obama in Washington when his fragile, 14-month-old "unity government", which took him five months to form in 2009, collapsed Wednesday.

The resignations followed the failure of regional powers to forge a deal to reduce tension over the UN-backed investigation into Rafik Hariri's 2005 assassination.

The tribunal prosecutor is expected to send draft indictments to a pre-trial judge this month, and Hezbollah leader Hassan Nasrallah has said he expects members of his party to be accused of involvement.

Hezbollah denies any role in the killing and had called on Hariri to withdraw Lebanon's funding for and cooperation with the tribunal — a demand which he rejected.

Arab League Secretary-General Amr Moussa said Lebanon's political crisis risks deteriorating further and all sides must work calmly to find a solution that allows justice to be served.

"We don't want Lebanon to move back to square one," Moussa told reporters in Doha, where he is attending a regional meeting. "We thought we had already left this station several years back."

Moussa said he was consulting with a number of Arab countries on the way forward, and was considering calling for a special meeting of the Arab League, although no decision had been reached yet.

"Perhaps we will leave it for individual intervention for the time being," he said.

Moussa, echoing US Secretary of State Hillary Clinton, said it was important that the special tribunal be allowed to continue its work, although he suggested any immediate move to hand down indictments naming Hezbollah could inflame the situation further.

"The tribunal should be above politics and justice should have its say and Lebanon must have a government," Moussa said. "But since we were waiting for several years, why not six more months of time in order to defuse the situation ... It is very threatening," he said.

But Moussa underscored that those responsible for Hariri's killing must be brought to book. "There was a crime, and the crime should be investigated and the criminals should be punished," he said.

A stalemate over the tribunal had crippled Hariri's government. The Cabinet had met, briefly, just once in the last two months and the government could not secure parliamentary approval for the 2010 budget.