Italian Prime Minister Silvio Berlusconi was jointly responsible for corruption by his Fininvest company in a 1990s battle to buy publisher Mondadori, a judge said in arguments for imposing damages on the firm.

A defiant Mr Berlusconi, now in the second year of his five-year term, vowed to remain in power until 2013 and said he would not be intimidated by what his supporters have called a "subversive plot" by judges to oust him.

"I am literally shocked," Mr Berlusconi said. "This ruling is beyond belief. This is a huge judicial blunder."

A Milan administrative court ruled at the weekend that Mr Berlusconi's holding company Fininvest must pay €750 million to CIR for bribing a judge in a 1990s battle to buy Italy's biggest publisher.

Mr Berlusconi had already been cleared at a criminal level in 2007 and therefore faces no further charges in the case.

But the Milan court, which published the explanation of its ruling yesterday, said Mr Berlusconi was nonetheless jointly responsible for corruption in the civil trial and therefore Fininvest should pay because he ran it at the time.

Aside from the massive damages claim, the Milan verdict has strong political overtones because CIR is owned by Mr Berlusconi's archrival Carlo De Benedetti, whose daily newspaper La Repubblica and weekly L'Espresso have led recent press coverage of the sex scandal involving the Prime Minister.

Mr Berlusconi's allies accused the judges in the case of timing the release of the ruling on damages in order to influence another ruling that could have far-reaching implications for his political tenure.

Italy's top court is meeting today to decide whether a law granting Mr Berlusconi immunity from prosecution while in office violates the Constitution. Should it decide that it does, trials against him that were suspended as a result will restart.

"The suspicious timing and the content of the ruling, 20 years after the events, reinforce the belief of those who, like us, think that there is an attempt to overturn the democratic choice of the Italian people," said top MPs from Mr Berlusconi's party in a joint statement.

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