Berlusconi and his supporters reacted angrily to his conviction and prison term, which was upheld Thursday. The decision marks the first time that Berlusconi, a three-time former prime minister and billionaire media mogul, has been definitively convicted of any crime, as all past rulings against him have been overturned on appeal or charges have expired.

Shortly after receiving the verdict, the 76-year-old billionaire took to Italian television to denounce the country's judicial system.

"It's hard to understand the violent attacks that have been bestowed upon me, with a series of charges and processes," Berlusconi said from his residence in the capital.

He also complained that his work as a public servant was not valued enough. "This is how Italy rewards the sacrifice and engagement of its best citizens," he said.

The Court of Cassation on Thursday - Italy's highest court - confirmed the conviction and four-year jail sentence. This would be reduced to one year under an amnesty.

Berlusconi appealed the ruling that was upheld by Italy's appeals court in May, following the original conviction last October. He was found guilty of involvement in a scheme that inflated the price of film distribution rights bought by his Mediaset business empire in order to avoid taxes, with him then pocketing the difference.

It is unclear whether Berlusconi would actually serve any time in prison, with community service or house arrest a likely option. However, his sentence cannot be imposed until the Senate votes to lift his parliamentary immunity, which is likely due in September. This allows him to remain as a senator and as leader of his center-right People of Freedom Party (PDL) for the moment.

He has declared he will continue his political activities and press for a reform of the justice system.

Shifting ground

Thursday's ruling has put the fragile cross-party coalition led by Prime Minister Enrico Letta under strain, even though Berlusconi has pledged his center-right party will continue to support the government.

After winning nearly a third of the vote in Italy's February general election, Berlusconi's party is now an influential member Letta's coalition.

On Friday, Letta urged lawmakers to act responsibly during this “sensitive” time. He repeated that Italy must have a stable government, saying the last thing it needs is to be worn down by partisan battles.

hc/dr (Reuters, AFP, AP, dpa)