Italy's parliament failed to elect a new state president in its first vote with deep splits in the centre left torpedoing a quick victory for its official candidate Franco Marini.
Marini, a former Senate speaker, won 521 votes, well below the required two-thirds majority of 672 of the 1,007 electors, comprising members of both houses of parliament and regional representatives.
A second ballot will be held later on Thursday and two votes a day will continue through the weekend if necessary.
Marini's clear failure, in a vote which is key to filling a government vacuum since the deadlocked general election in February, was a slap in the face for centre-left leader Pier Luigi Bersani. He badly split his party by nominating Marini in a deal with centre-right boss Silvio Berlusconi.
Many rebellious centre-left parliamentarians voted in the secret ballot for academic Stefano Rodota, candidate of the populist 5-Star Movement of former comic Beppe Grillo.
Rodota won more than 240 votes and there were also more than 100 blank or spoilt ballots.
Nichi Vendola, head of Bersani's leftist ally SEL, said nominating Marini "was a mistake. The result was worrying. Marini was a candidate who united the centre right, not the centre left."
He said unless things changed, his 46 representatives would keep voting for Rodota.
Roberto Fico, from Grillo's movement, said: "The Berlusconi-Bersani marriage did not work, so the consensus behind Rodota is growing."
After three rounds of voting, only an absolute majority is required but the chances for Marini, 80, may decline as time passes, wrecking Bersani's deal with Berlusconi which is aimed at helping him form a minority government.
Bersani has repeatedly refused to agree to Berlusconi's demands that they form a broad coalition government together. But it is widely believed he wants to parley an agreement on the presidency with centre-right willingness to support a minority centre-left government.
FURY ON LEFT
The vote for a successor to President Giorgio Napolitano, whose term ends on May 15, is a crucial step towards resolving the stalemate since an inconclusive election in February which left no party with enough support to form a government.
However the choice of Marini provoked fury in Bersani's Democratic Party (PD) and an open revolt by his rival, Matteo Renzi, the 38-year-old mayor of Florence.
Renzi described the 80-year-old Marini as "a candidate from the last century" who had no charisma or international standing, adding that he was only chosen because he was acceptable to Berlusconi.
"The PD is in fragments, it doesn't exist anymore," Renato Brunetta, the parliamentary leader of Berlusconi's People of Freedom (PDL) party, told Canale 5 television.
Until the new president is elected, the paralysis that has hobbled attempts to form a government for more than 50 days since the election will continue.
The PD, which controls the lower house of parliament, has the largest number of presidential electors with 430, ahead of Berlusconi's PDL with 211 and the 5-Star Movement with 162.
If no candidate succeeds in the initial rounds, the required threshold drops to a simple majority from the fourth round. But it is unclear whether Marini would remain in the race or drop out if he failed to secure the two-thirds majority.
That could lead to the PD abandoning hopes of a deal with the centre right and going for a candidate like former Prime Minister Romano Prodi, one of Berlusconi's oldest political enemies. Such an outcome is widely seen as likely to lead to an election within months.
The head of state is a largely ceremonial figure but has a number of vital political functions, as Napolitano demonstrated in 2011 when he put Mario Monti at the head of a government of technocrats to replace the scandal-plagued Berlusconi.
It will be up to the new president to end the political deadlock left by the election, either by persuading the parties to come to an accord that would allow a government to be formed or by dissolving parliament and calling a new national vote.
February's election gave Bersani's centre-left alliance control of the lower house of parliament but short of the Senate majority it needed to form a government.
The 61-year-old former industry minister has faced growing pressure from Renzi and others in his party after throwing away a 10-point opinion poll lead before the vote.
While the fiery Grillo remains firmly opposed to the main parties, agreement over the candidacy of Marini could signal greater willingness on the part of Bersani and Berlusconi to come to an understanding that would avert immediate new elections.
However Brunetta said the revolt in the PD ranks suggested the prospects of a government accord being reached remained highly uncertain.