Brazil's supreme court said Cesare Battisti should be freed immediately [Reuters]

Italy has said it will appeal a decision by Brazil's highest court to stop the extradition of an Italian fugitive convicted of four murders in the 1970s.

It vowed to take its case to the International Court of Justice after Cesare Battisti, a former far-left fighter in Italy, walked free on Thursday.

Silvio Berlusconi, the Italian prime minister, denounced the decision by Brazil's supreme court while the country's youth minister said it was "a slap in the face for Italian institutions, an act unworthy of a cvilised and democratic nation".

Franco Frattini, Italy's foreign minister, said Italy would "activate every possible judicial mechanism ... in particular through the International Court of Justice in The Hague, the Netherlands.

Brazil's nine member court ruled by a 6-3 majority that the decision take by Luiz Inacio Lula da Silva, the former president, to deny the Italian extradition request and authorise Battisti to remain in Brazil complied with a bilateral treaty.

Battisti, 56, a former member of the radical Armed Proletarians for Communism (PAC) group, became an international fugitive after escaping from an Italian jail in 1981 and spent decades evading justice living in Mexico, France and Brazil.

He was convicted in his absence by an Italian court in 1993 for the murders of four people in the 1970s, charges he has denied, and sentenced to life imprisonment.

Political refugee

Brazil granted him political refugee status in January 2009, in a move that effectively halted extradition proceedings.

But eight months later, the supreme court nullified that decision and said it favoured extraditing him to Italy after all, at the same time ruling that Lula should be the final arbiter.

In late December 2010, Lula, in his last moments in office, enraged Berlusconi by denying the extradition.

The Italian government appealed, and Brazil's nine supreme court justices discussed the legality of Lula's decision on Wednesday.

The court also ruled by 6-3 that Italy did not have legal standing to challenge Lula's decision.

"At stake here is national sovereignty. It is as simple as that," Judge Luiz Fux said, to justify his vote against Battisti's extradition and in favour of his release.

Battisti has insisted that he is innocent.

One of his lawyers, Renata Saraiva, told the daily O Globo he was "very anxious" as he awaited the ruling, taking anti-depressant medication to handle the stress.

It remained unclear if the current president, Lula's successor Dilma Rousseff, will still have the ultimate say in the case.