Italy's Constitutional Court on Wednesday threw out a law that shielded Prime Minister Silvio Berlusconi from prosecution while in office, paving the way for corruption proceedings to resume against him.
A defiant Berlusconi slammed the court as primarily "left-wing" and vowed to see out his five-year mandate won in April 2008, saying he had the support of 70 per cent of the Italian people.
The combative media tycoon also took a swipe at the media, which he said was "72 per cent left-wing", and traded barbs with President Giorgio Napolitano, questioning the former communist's impartiality.
Berlusconi's cabinet ministers and his main ally, Northern League leader Umberto Bossi, closed ranks behind the premier, who is already under fire over allegations over his private life including links to call girls.
"We won't give up," said Bossi, who was with Berlusconi when the court ruling was announced.
Berlusconi, 73, said he expected the ruling "because with a Constitutional Court with 11 left-wing judges it was impossible for them to approve" the law passed last year shortly after he returned to power for a third time.
"We must govern for five years with or without the law," the billionaire prime minister told reporters outside his Rome residence.
In the rare exchange between Berlusconi and Napolitano, the prime minister said testily: "We know what side the president is on."
The remark drew a response from the president's office saying Napolitano "is on the side of the constitution, and he exercises his duties with absolute impartiality, in a spirit of loyal cooperation with the institutions."
Hitting back, Berlusconi said: "I'm not interested in what the head of state said... Period."
Napolitano, 84, a former member of the Italian Communist Party, was among the leading architects of the party's transformation into a social-democratic movement.
The law thrown out Wednesday shielded the holders of Italy's four top political jobs -- prime minister, president and the speakers of the two houses of parliament -- from prosecution while in office.
The 15-member Constitutional Court ruled that the law violated the constitutional guarantee of equality before the law.
Former anti-corruption judge Antonio di Pietro, now head of the small Italy of Values party, called on Berlusconi to "stop making laws for his personal use and step down".
Berlusconi now faces at least two legal battles, which he dismissed as "authentic farces" while vowing to fight his accusers in court.
In one case, the conservative premier is accused of paying his British former tax lawyer, David Mills, 600,000 dollars (400,000 euros) to give false evidence in two trials in the 1990s.
Mills, who was tried separately, is appealing a guilty verdict delivered in February, when he was sentenced to four and a half years in jail.
Another case involves allegations that Berlusconi's Mediaset television empire inflated figures for its purchases of broadcasting rights in order to create slush funds.
Berlusconi's battles with the law have marked his public life since he burst onto the political scene in the mid-1990s.
He has faced charges including corruption, tax fraud, false accounting and illegally financing political parties.
Although some initial judgments have gone against the tycoon, he has never been definitively convicted.
Titillating scandals such as Berlusconi's relationship with an 18-year-old aspiring model -- prompting his wife to seek a divorce -- and an allegation that he spent a night with a call girl have dominated headlines in recent months.
Berlusconi is also reeling from a weekend court ruling that his Fininvest holding company must pay 750 million euros (one billion dollars) to a rival media group.
He was found "co-responsible" for the bribery of a judge who decided in favour of the holding company during its takeover battle with Compagnie Industriali Riunite for the Mondadori publishing house.
Analysts believe Wednesday's court ruling further weakens Berlusconi.
"The ferocity of Berlusconi's attacks is a sign of weakness," said Giacomo Marramao, a Rome-based political philosophy professor.
He said the prime minister's "public image was seriously dented by the media hype" over the call girl allegations and his relationship with the teenage model, with the constitutional court ruling to damage it further.
"The political climate risks heating up," said Marco Tarchi, a political science professor in Florence. "We're going see an exacerbation of tensions, taking into account Berlusconi's very strong and personal reactions."