A significant number of young women prostituted themselves with Italian Prime Minister Silvio Berlusconi, prosecutors investigating him said in a document made public on Monday.

The prosecutors also believe that Berlusconi gave some women free use of a string of apartments in a residential complex near Milan in exchange for sex, according to the document posted on the website of the lower house of parliament.

It details accusations levelled by magistrates, who are probing whether Berlusconi paid to have sex with 17-year old Karima El Mahroug, a nightclub dancer better known under the stage name Ruby.

Prosecutors sent the document to the lower house to justify their request to search the office of a Berlusconi associate who they believe paid the women on behalf of the 74-year old premier. A special parliamentary committee is due to decide this week whether to allow or reject the request.

Berlusconi denies any wrongdoing, says the allegations are absurd and accuses the magistrates of acting illegally for political motives.

He said on Sunday he had never paid for sex and was in a stable relationship since separating from his second wife.

The conservative leader has seen off a series of sex scandals since breaking up with Veronica Lario, who filed for divorce in 2009 saying she could no longer be with a man frequenting minors.

But the latest incident comes at a difficult time for Berlusconi, who no longer enjoys a secure parliamentary majority since a split last year with former ally Gianfranco Fini.

He narrowly scraped through a confidence vote last month, and last week Italy's top court struck down part of a law that gave him immunity from prosecution, leading some commentators to predict that the country would head to early elections.

The prosecutors' document says that Nicole Minetti, a Lombardy regional official who was formerly Berlusconi's dental hygienist, recruited a significant number of young women, who prostituted themselves with Silvio Berlusconi. Minetti, who is also under investigation, denies the accusations.

FLATS FOR SEX

The document said that El Mahroug had told prosecutors that some women had been granted free use of apartments in Milano Due, a leafy residential neighbourhood on the outskirts of Milan that media tycoon Berlusconi built during a 1970s property boom.

On this point the investigation has revealed ample evidence, it said, listing the names of eight women whose apartments were searched by police.

The probe focuses on El Mahroug, who says she received 7,000 euros ($9,318) after attending one of Berlusconi's parties at his sumptuous villa near Milan. Prosecutors allege that she went to Berlusconi's residence several times between February and May 2010, when she was 17, and that he paid to sleep with her.

Having sex with a prostitute aged under 18 is an offence in Italy. El Mahroug says she did not sleep with the premier but her use of the term bunga bunga, describing sex parties, captured the imagination of headline writers around the world.

The magistrates also allege that Berlusconi put pressure on police officers to let her go after she was detained over theft allegations in an unrelated case. He has acknowledged making a phone call to the police, but says he was merely helping a person in need and did not exert any improper influence.

The prosecutors have said they will request a fast-track trial for Berlusconi -- something they usually do when they believe they have substantial evidence. They have summoned Berlusconi for questioning at the end of this week, but his lawyers say they have not decided whether he will attend.