Populist leader Beppe Grillo on Wednesday ruled out voting for any government led by the traditional parties after Italy's inconclusive election but said his 5-Star Movement could back individual laws.
Democratic Party (PD) leader Pier Luigi Bersani, whose center-left coalition took the most seats in parliament but failed to win a majority in the vote which ended on Monday, has put out cautious feelers towards 5-Star, which benefited from a huge protest vote.
But Grillo, who holds the balance in parliament, slammed the door in Bersani's face and poured insults on him and other center-left leaders on his blog. He accused Bersani of making "indecent" proposals to his anti-establishment movement.
The fiery comic and blogger called Bersani "a dead man talking," and political stalker, saying he should have resigned after falling badly short in the election which pollsters had expected the center-left to win.
No party has enough seats to govern after the vote which threw Italy into political limbo and rattled global investors worried by the threat of a new euro zone crisis.
Grillo said on Twitter that 5-Star "will not give any vote of confidence in the Democratic Party (PD) or anybody else but will vote in the chamber for laws which reflect its program".
He recalled a string of anti 5-Star comments by Bersani during the election campaign and added on his blog: "He has the arrogance to ask for our support."
As part of overtures on Tuesday that were seen as aimed at Grillo, Bersani laid down an agenda of measures mostly in line with the 5-Star program.
But he said any groups backing a center-left government must support a vote of confidence - required when a new administration takes office.
He responded to Grillo's insults only by saying he should come to the new parliament and "assume his responsibilities."