Italy could be inching closer towards another election within months after centre-left leader Pier Luigi Bersani issued an ultimatum to anti-establishment Five Star Movement boss Beppe Grillo to support a new government or return to the polls.
Last week's inconclusive election, in which Mr Grillo won a huge protest vote, left no group with a working majority in parliament, making an alliance with a rival the only way out.
In an interview on RAI state television late yesterday, Mr Bersani underlined his opposition to two of the options currently being floated - another technocrat government like the outgoing one led by Mario Monti or a grand coalition with Silvio Berlusconi's centre-right.
That would leave only one possibility to avoid elections - Mr Grillo's backing for the centre-left, which won the lower house in the election but does not have enough support to rule in the Senate.
"Now (Grillo) must say what he wants, otherwise we all go home, including him," Mr Bersani said.
Mr Grillo has repeatedly said his populist movement, which he refuses to call a party, would not give a vote of confidence to any government of established parties, although it could support individual laws.
"We have already said it several times: we won't give a vote of confidence to a government of political parties," the movement's newly named Senate leader, Vito Crimi, told its novice politicians today during a meeting in Rome streamed on Mr Grillo's blog.
At the meeting, the parliamentarians introduced themselves to each other and the public, some betraying their nervousness in the spotlight with shaky voices.
The uncertainty in Italy, during a long limbo before talks to form a government begin after March 15th, has unsettled international markets.
The spread between Italian 10-year benchmark bonds and German bunds - a measure of investor confidence - widened on Monday to an almost three-month high as the country entered its second week of gridlock.
Mr Grillo last week called Mr Bersani a "dead man talking" when he first made overtures to the 5-Star Movement, which became Italy's single biggest party in its first national test, taking a quarter of the vote. Mr Bersani's ultimatum may not work against Mr Grillo and his tactics are apparently opposed by some of the leadership of his Democratic Party (PD).
The Genoese comic is widely believed to want to get back to the polls to wipe out the old order and boost his vote. He is also believed to fear his novice politicians could be suborned by cynical traditional politicians once they get into parliament.
"It's in his interest to go back to the ballot box as soon as possible," said Maurizio Pessato, vice chairman of polling institute SWG.
"Grillo can't win more than 8 million votes promising to get rid of the establishment and then immediately ally himself with the old guard," he added.
Nichi Vendola, leader of the leftwing SEL party which is allied with Mr Bersani, criticised Mr Grillo today, accusing him of trying to win more votes by rejecting an alliance.
"Even he is at a crossroads. Either he accepts the challenge of a radical transformation of our country or he will be more of a politician than the others," Mr Vendola said.
"If there is no agreement, it is better to return to the polls," Mr Vendola added on his Facebook page.
Reuters