Italian media mogul and former prime minister Silvio Berlusconi is under investigation for alleged links with a series of bombings perpetrated by mafia groups in the country in 1992 and 1993.

At least ten people were killed in bomb attacks in Rome, Florence and Milan. Sicilian mafia syndicate Cosa Nostra are believed to have been behind the murders, thought to be in retaliation for the arrest of mafia boss Toto Riina. High-profile killings include those of anti-mafia prosecutors Giovanni Falcone and Paolo Borsellino and politician Salvo Lima.

Prosecutors in Florence opened the probe into Berlusconi and the co-founder of his party Forza Italia (Go Italy), Marcello Dell'Utri, following a wiretapped conversation in which jailed mobster Giuseppe Graviano claimed the ex-premier suggested he carried out attacks against the state.

"Berlusconi asked me for this favour, this explains the urgency," Graviano was heard telling a fellow inmate last year, La Repubblica reported.

Graviano is serving several life sentences for his role in the attacks.

Berlusconi's lawyer Niccolò Ghedini said the claims were "defamatory allegations" that surfaced ahead of general elections next year. He added the ex-prime minister never had any contact with Graviano.

"It is clear that this is the umpteenth investigation that can only end by being rapidly shelved, as previously happened in the past, as there are no really new elements," Ghedini said in a statement quoted by news agency Ansa.

Prosecutors in Florence had already opened two investigations into Belusconi's alleged involvement in the attacks. The last probe was closed in 2011 due to lack of evidence.

Berlusconi founded his first media group in the late 1970s and Italy's first three private TV channels in the following years. He became the owner of football club AC Milan in 1986.

By the time he started his political career with the founding of Forza Italia in 1994, Berlusconi had already been investigated for alleged corruption during the Mani Pulite (Clean Hands in Italian) inquest, which he survived.

He reportedly told journalists Indro Montanelli and Enzo Biagi he was forced to enter politics to avoid imprisonment.

Dell'Utri is already serving time in jail after he was found guilty of, among other crimes, complicity with Cosa Nostra.