Italian protest party leader Beppe Grillo on Thursday slammed the right-left deal to back former trade union leader Franco Marini for president saying he was "a man of the system".
Marini's election "would be a disaster", Grillo told AFP in an interview.
"He was a Christian Democrat, a trade unionist, a speaker of the senate, he is a man of the system," said the ex-comedian, who leads the anti-establishment Five Star Movement party which won a quarter of the vote in February elections.
"He is a president who is a judicial guarantee. He's chosen by Berlusconi. He'll guarantee that Berlusconi stays in place," Grillo said, referring to two ongoing trials against the scandal-tainted billionaire tycoon.
Condemning the agreement between leftist leader Pier Luigi Bersani and Berlusconi announced on Wednesday, Grillo said: "The leaders of right and left met at night in a room to decide the fate of 60 million people".
But Grillo did not dismiss the chances of the candidate supported by his party, academic and civil rights advocate Stefano Rodota.
"We'll stick with Rodota... If someone wants to vote for him great, we can collaborate," he said.
Grillo was speaking during a campaign stop in the Friuli Venezia Giulia region in northeast Italy ahead of local elections there.