ROME — Allegations that Prime Minister Silvio Berlusconi hooked up with prostitutes he kept in rent-free luxury apartments have weakened the government and damaged the country's image abroad, experts say.

Italian magistrates on Friday announced an enquiry into the relationship between Berlusconi and an underage girl, known as Ruby, as the prime minister was still reeling from a court ruling partially stripping him of political immunity.

While having sex with prostitutes is not a crime in Italy, having sex with a minor is illegal.

On Monday Milan prosecutor's office made public a document with evidence that "a significant number of young girls prostituted themselves with Silvio Berlusconi in his residences in exchange for sums of money."

Prosecutors have also collected wire-taps, leaked to the press, revealing details about sleazy parties held at the prime minister's homes.

"It's a very serious document, the prime minister's image will be weakened abroad. It's not a situation that will be easily managed," Franco Pavoncello, political science lecturer at the John Cabot Univeristy in Rome told AFP.

"The accusations are very serious indeed and will have repercussions on a political level considering the current weakness of the government.... it's likely to lead to early elections," he said.

The prosecutors claim to have obtained "ample proof" which would warrant a probe into the addresses which the 74-year-old Berlusconi loaned rent-free to young women who attended parties thrown at his residence near Milan.

Ruby, real name Karima El Mahroug, "frequented Berlusconi's Arcore residence (in Milan) between February and May 2010", according to the public prosecutor who says there is evidence to prove this, including mobile phone traces.

In wire taps ordered by Milan's prosecutors of conversations between Ruby and her friends, the Moroccan, now 18, said she had asked Berlusconi for five million euros in compensation for having dirtied her name.

Berlusconi has not yet publicly responded to the document released on Monday. In a video message released Sunday he raged against the "laughable, unfounded accusations", saying he had "had a stable relationship" since splitting up with his wife, Veronica Lario, in 2009.

Roberto D'Alimonte, lecturer in political sciences at Luiss University in Rome, said the country now found itself in "a difficult moment, full of uncertainty," but said this latest conflict between Berlusconi and Milan's prosecutors would probably not affect the prime minister's position.

"Silvio Berlusconi is a libertine, the most libertine of all the G8 leaders, but libertinism is not a crime. In Italy it's not even a political consideration, his voters elect him anyway," he said.

"In any case, this scandal won't change the country's image at all. Silvio Berlusconi has been embarrassing for the past 15 years. He has been compromising Italy's image since he entered into politics in 1994," he added.

President Giorgio Napolitano said in a statement Tuesday he was "well aware of the turmoil of public opinion" and hoped the Milan's prosecutor's office would "finish verifying the results of the enquiry as soon as possible."

Fabrizio Cicchitto, head of the opposition PDL party in the Chamber of Deputies, said "we will see whether there are the necessary conditions to carry on the government's activities... or whether we should go to an early vote to defend everyone's freedom."

Italian media voiced the country's embarrassment.

"If the magistrates don't manage to prove there was a crime, we're still left with the image, with the moral question, for Italy and our credibility abroad," the Repubblica daily said.

"Italy doesn't deserve... an electoral campaign played out entirely on the prime ministers vices and the procession of real or supposed escorts on television and in the newspapers," Il Messaggero wrote.

Berlusconi, a notorious womaniser, admits that he is "no saint" but has said he never paid for sex. Both he and Moroccan-born Ruby, a disco dancer, have denied having had sexual relations.