Just two days after announcing he won't run in spring elections, former Italian premier Silvio Berlusconi was convicted of tax fraud and sentenced to four years in prison Friday in a verdict that could see him barred from public office for five years.

Berlusconi, after dominating Italian politics for nearly two decades, has seen his power weakening in the last year as a sex scandal tarnished his image and he was forced to resign as premier after failing to convince financial markets that he could come up with convincing reforms to shield Italy from Europe's debt woes.

In the latest blow, the 76-year-old billionaire media mogul received the stiffest sentence among the four co-defendants convicted in a scheme that involved inflating the price his media empire paid for TV rights to U.S. movies and pocketing the difference. The sentence was more than the three years and eight months sought by prosecutors.

The court, which began hearing the case in 2006, also said Berlusconi could not hold public office for five years or manage any company for three years, penalties that would take force only if the conviction is upheld on two levels of appeal.

Plans to appeal 'unreal' conviction

In a statement, Berlusconi's lawyers condemned the verdict as "absolutely incredible," and said they would appeal. Berlusconi is expected to remain free while two levels of appeal are exhausted.

However, a corruption bill drafted by the technical government headed by Premier Mario Monti, who replaced Berlusconi, would bar anyone convicted at the trial level from seeking office.

People hold pictures of Italy's former prime minister Silvio Berlusconi with words that read You Never Forget Your First Time, as they celebrate after Berlusconi was sentenced to jail for tax fraud in downtown Rome on Friday. (Alessandro Bianchi/Reuters)

Berlusconi denounced the conviction as "unreal" and the case as politically motivated — as he has the numerous charges against him mostly for business dealings since entering political life in 1994.

Berlusconi stayed away from the Milan tribunal, where his lawyers on Friday were defending him in a separate courtroom on charges of having paid for sex with an underage Moroccan teen and trying to cover it up.

'Incredible and intolerable' , says Berlusconi

"It is a political conviction that I can define perfectly well as incredible and intolerable," Berlusconi said in a phone call to his Italia 1 private network Friday evening.

He denied that there was any connection between his decision to step aside and allow another centre-right candidate to seek the premiership in spring elections.

"My lawyers and I never thought that such a conviction would be possible," Berlusconi said.

The court read its reasons for the conviction immediately in court, a rare occurrence given they have 90 days to write them. It was a sign that the judges want to speed the case along to the appellate level before the charges expire, sometime next year or early 2014.

'My lawyers and I never thought that such a conviction would be possible'—Silvio Berlusconi

"He has been around this particular block more than a few times," said Alexander Stille, who has written several books on Italy. `'I don't see — partly given his advanced age and the nature of power in Italy — him doing jail time."

Berlusconi has been convicted in the past at the trial level. But the convictions have always either been overturned on appeal or seen the statute of limitations run out.

Roberto D'Alimonte, a political science professor at Rome's LUISS University, said Italians won't change their minds based on the conviction.

"Foreigners will be surprised, but not Italians," D'Alimonte said.

The real impact will be in whether the provision barring those convicted at the trial level from office will make it through Parliament in the corruption bill.

"It is something to monitor," D'Alimonte said.

11 people on trial

Prosecutors allege the defendants were behind a scheme to purchase the rights to broadcast U.S. movies on Berlusconi's private television network and falsely declared the payments to avoid taxes. They said the defendants then inflated the price for the TV rights of some 3,000 films as they relicensed them internally to Berlusconi's networks, pocketing the difference amounting to around €250 million.

A total of 11 people were on trial.

Three were acquitted, including a close associate of Berlusconi, Fedele Confalonieri, chairman of Mediaset.

Berlusconi and three others were convicted, including a Hollywood producer, Frank Agrama, who received a three-year sentence. The four convicted must deposit a total of €10 million into a court-ordered fund while the appeals proceed.

Four defendants were cleared because statute of limitations had run out on their charge.