Italy's former prime minister Silvio Berlusconi attends a news conference in Rome in this November 25, 2013 file photo.[Photo/Agencies]

ROME - Italy's supreme court on Tuesday upheld former Prime Minister Silvio Berlusconi's acquittal from charges of having sex with an underage prostitute and abusing his power to cover it up.

The supreme court issued its decision after nine hours of a closed session. According to the Italian law, the Rome-based court will give explanations about the ruling within 90 days.

A lower court in Milan in 2013 had convicted the three-time premier and media tycoon of both charges, and sentenced him to seven years in prison and a lifetime ban from political affairs, after a two-year-long trial composed of 50 hearings. But an appeals court overturned the decision last year.

Berlusconi had been accused of paying for sex with an underage former Moroccan dancer, Karima El Mahroug, better known as "Ruby Heartstealer," when she was 17 and phoning to a police station when he was prime minister in May 2010 after she was detained on an unrelated theft accusation.

The then prime minister allegedly told police that El Mahroug was a niece of Egypt's then President Hosni Mubarak, which was actually not true, and pressured officials to release her to avoid diplomatic tensions between the two countries.

Both Berlusconi and El Mahroug denied ever having sex. Dozens of showgirls, however, have described sex parties at Berlusconi's houses that young women were paid to attend.

A separate investigation connected to the Ruby case is being carried out by Milan prosecutors over whether Berlusconi paid witnesses to give false testimony. And another trial has also been started in Naples, a city in southern Italy, on him allegedly bribing former senators to change political sides.

Meanwhile, Berlusconi last week ended his community services for a tax fraud verdict 45 days earlier than planned because of his good behavior in helping the elderly and the disabled at a non-profit facility and in apologizing to Italian judges for making accusations against them.

But given his numerous legal troubles and old age, experts believe Berlusconi, who at 78 is still the leader of Forza Italia (FI), a center-right opposition party in parliament, will likely not be able to run for the Italian government or parliament again.

In a recent interview with Xinhua, Peter Gomez, co-founder and columnist of the Il Fatto Quotidiano newspaper, explained that Berlusconi has been banned from holding public office until 2019 according to a law adopted by the government of then Prime Minister Mario Monti in 2013.

In principle, Gomez elaborated, under the Italian law Berlusconi may obtain "rehabilitation" -- meaning good behavior combined with a declaration that his tax-fraud verdict, his first-ever final guilty conviction, has become extinct -- and become able to run for elections in the spring of 2018.

"But in practice Berlusconi's re-election is not likely to happen amid his many legal troubles," he noted.

Berlusconi, who has always denied any wrongdoing and insisted on being the victim of left-wing prosecutors since he entered politics in 1994, has faced multiple fraud and corruption trials. He resigned in November 2011 in disgrace sparked by the Ruby case and other scandals.