Italy's highest court has upheld ex-premier Silvio Berlusconi's tax fraud conviction but ordered a review of a five-year ban on public office that was part of the lower court's sentence.

The court today confirmed the four-year prison sentence, and ordered another court to determine the length of a public office ban.

This is the first time Berlusconi, a three-time former premier and billionaire media mogul, has been definitively convicted of any crime.

Another court will now have to determine the length of a public office ban. A state prosecutor had recommended this week that the political ban be reduced to three years because of conflicting laws on public office bans.

Berlusconi is unlikely to actually go to prison. Three years will be shaved off as part of a general pardon aimed at easing prison crowding, and it is unusual for defendants to serve sentences of just one year for a first offence, particularly at Berlusconi's age.

But his conviction heightens pressure on premier Enrico Letta's fragile coalition government as some in the centre-left may find it unpalatable to continue in a government with a party whose leader has been convicted of a crime.

Berlusconi, 76, awaited the sentence at his residence in central Rome with his lawyers, deputy party leader Angelino Alfano and his eldest daughter, Marina, all of whom were seen entering the building in the hours leading up to the announcement.