ROME (AFP) - Italian prosecutors on Monday asked that former Prime Minister Silvio Berlusconi be banned from politics forever and serve six years in prison for having sex with an underage prostitute and abusing his official powers.

"There is no doubt that Silvio Berlusconi is guilty of the crimes he is accused of," prosecutor Ilda Boccassini told the courtroom in Milan at the close of a two-year trial that could rock the country's newly-formed grand coalition government.

"He had sex with her and he knew she was a minor," said the prosecutor.

"We request a sentence of six years in prison," she said. "We ask for a perpetual ban from holding public office."

The trial relates to alleged crimes in 2010 when Berlusconi was still prime minister and revolves around alleged raunchy "bunga bunga" parties at his luxury residence outside Milan.

"The women invited to the then prime minister's private residence were part of a prostitution system set up for the personal sexual satisfaction of the defendant," Ms Boccassini said.

Berlusconi's defence lawyers will now have a chance to present their final arguments on June 3.

The verdict could come at the hearing after that, which has been scheduled for June 24.

Both the now 76-year-old Berlusconi and the woman involved have denied ever having sex for money.

Berlusconi is accused of paying for sex on several occasions with Moroccan-born Karima El-Mahroug, a then 17-year-old exotic dancer nicknamed "Ruby the Heart Stealer" who was spotted by one of his associates at a beauty contest in Sicily in 2009.

Ms Boccassini said El-Mahroug quickly become the premier's "favourite" and had not admitted the relationship with him only because she had received as much as 4.5 million euros (S$7.23 million) from the flamboyant billionaire tycoon.

Ms Boccassini said El-Mahroug had followed a "negative Italian dream" based on money.

It is also alleged that Berlusconi called a police station to pressure for El-Mahroug's release from custody when she was arrested for petty theft - an abuse of the office of the prime minister.

According to prosecutors, he did so because he was fearful she could reveal their liaison.

His defence claims he believed El-Mahroug was the niece of former Egyptian president Hosni Mubarak and wanted to avoid a diplomatic incident.

Berlusconi and his supporters say the trial is only the latest example of "judicial persecution" by left-wing prosecutors in Milan out to get him.

A programme on Sunday on a television channel he owns included interviews with Berlusconi and El-Mahroug in which the two spoke of "perfectly normal" soirees that had been wrongly portrayed.

Berlusconi has claimed in the past that performances by girls in a basement discotheque after dinner were in fact "burlesque contests".

Prosecutors and some of the attendees have said they were hardcore strip shows followed by sexual encounters with the participants.

The legal woes are straining relations within Prime Minister Enrico Letta's coalition government in which Berlusconi's People of Freedom party is a crucial partner.

Moderate leftist Letta reacted angrily over the weekend when Deputy Prime Minister Angelino Alfano attended a rally against the judiciary in which Berlusconi also took

part on Saturday.

Berlusconi has been under investigation or on trial ever since entering politics in the 1990s after a career in construction and media.

Three of Berlusconi's friends - a showbusiness agent, a former network anchor and a former regional assemblywoman - are on trial on pimping charges in a separate trial linked to the case.

El-Mahroug, who has not spoken at Berlusconi's trial, is due to testify at that trial on Saturday.