ROME -- Former Premier Silvio Berlusconi, who announced this week he wouldn't run in spring elections, pulled an about-face Saturday and said he felt compelled to stay in politics to reform Italy's justice system after being convicted of tax fraud.

Berlusconi's comments came hours after a Milan court sentenced him to four years in prison and barred him from public office for five years after convicting him in a decade-old case involving the purchase of TV rights of U.S. films for his media empire.

And they came a day before Berlusconi's beleaguered People of Freedom party heads into a regional election in Sicily seen as a test of its ability to pull itself back together after Berlusconi's fall from grace last year and a series of local political corruption scandals that have soured Italians on their entire political class.

The Sicily vote is also a harbinger of what Italy may witness in the spring as voters go to the polls for a general election amid recession and a political transition that has seen comic Beppe Grillo's populist Five-Star Movement threaten Italy's traditional center-right and center-left parties.

Friday's sentence isn't definitive until all appeals are exhausted, and Berlusconi's lawyers vowed to appeal. He remains free and is unlikely to serve any jail time anyway given his age -- 76 -- and the possibility that the statute of limitations may expire before the two levels of appeals are completed.

But Berlusconi nevertheless denounced the judges as politicized, as he has done in his many legal wranglings with Italian magistrates ever since he entered politics in 1994.

He told his private Mediaset television Saturday that the verdict would have consequences.

"I feel obliged to stay in the game to reform the justice system so that what happened to me doesn't happen to others," he told TG5. He didn't elaborate or say in what capacity he would work, but he planned to speak publicly later Saturday.

Berlusconi has wavered about his political future in the year since he was forced from office amid sex scandals and his inability to reassure financial markets that he could push through the economic reforms needed to ward off a Greek-style debt crisis.

Premier Mario Monti was tapped to head a technical government, which has pushed through a series of tax hikes, structural reforms and austerity measures that, while hurting ordinary Italians, have significantly brought down Italy's borrowing rates.

On Saturday, Italians in several cities took to the streets for a "No Monti" day of protests.

Monti had initially said he wouldn't run in spring elections, but recently hinted that he could stay on for a second term under the right circumstances. Berlusconi had even come out and supported Monti after saying he wouldn't seek a political comeback.

But apparently things changed after the billionaire media mogul received the stiffest sentence among the four co-defendants convicted Friday in a scheme that involved inflating the price his Mediaset media empire paid for TV rights to U.S. movies and pocketing the difference.

Berlusconi called the conviction "absurd" and said if a country can't count on impartial judges, it ceases to be a democracy.

During his three stints as premier, Berlusconi had sought to reform Italy's notoriously slow and inefficient judiciary. In the absence of a wholesale reform, his forces in parliament passed several laws designed to help him and his colleagues in their legal woes, including passing immunity bills that temporarily halted trials against him.