ROME (Reuters) - Prime Minister Silvio Berlusconi faced more pressure to resign on Thursday after magistrates issued new documents with fresh details of erotic parties, some with under-age girls, and of his gifts to participants.

The center-left opposition said the new documents made his position "untenable" and said he should resign willingly or that his conservative allies should put pressure on him to step aside for the good of the country.

The 227 pages of new documents were sent by Milan magistrates to parliament on Wednesday night and chunks were leaked to Italian media, which published excerpts on Thursday.

They say that a second woman who attended the parties was under-age at the time, in addition to a Moroccan dancer at the center of the inquiry who was 17 when some of the parties were held.

They also show that a key Berlusconi associate who is being investigated on suspicion of procuring prostitutes is privately turning against him and made disparaging remarks about his physique and age in phone conversations taped by police.

The magistrates have so far sent more than 600 pages of documents to parliament to support their request to search the office of Berlusconi's accountant, who is suspected of dispensing money and gifts to the women.

Asked about the new leaks, Berlusconi responded late on Wednesday that the investigation was itself "scandalous."

One of Berlusconi's most loyal allies, Foreign Minister Franco Frattini, rejected suggestions that the center-right government should dump Berlusconi because of the scandal.

He said Berlusconi's PDL party "does not have its hands free to change its leader without (general) elections."

"It would be absolutely mistaken to think of a change of leadership," Frattini told a lunch of foreign correspondents, saying Berlusconi had been chosen directly by voters at the last election in 2008.


He conceded that the scandal had damaged Italy's image abroad but said this was the fault of politicized, biased magistrates and not Berlusconi, saying the evidence of many people showed the allegations were false.

Excerpts in Italian media of transcripts of police interrogations of the women and phone wiretaps describing wild parties emerged just two days after Berlusconi's lawyers filed documents insisting the encounters were just friendly dinners.

Frattini said Italy's stability required that it continued with Berlusconi as leader--and in any case no opposition figure could beat him in elections.

In verbatim transcripts published by at least two Italian news agencies and several newspapers, a woman named Maria told magistrates that in June 2010, a Berlusconi associate invited her to a party at the prime minister's villa near Milan.

"After the dinner, the prime minister said 'now we are going to do some bunga-bunga," the term magistrates say the participants used to describe their parties.

Maria says she did a belly dance while another young woman walked around the room dressed only in a bra and panties. Maria told magistrates a Brazilian woman wearing thong underwear danced a "hard version of a samba" as the men watched.

"Even the other girls danced, showing their breasts and their bottoms and they all went near the prime minister who touched them in their intimate parts," the news agencies and newspapers quote Maria as telling magistrates.

The Milan prosecutors say Berlusconi paid for sex with prostitutes at the parties, including a teenage nightclub dancer whose stage name is "Ruby the Heart Stealer."

Berlusconi denies wrongdoing and says he never paid for sex.

When police searched the apartment of one of the women they investigated, they found money and jewelry, which she told the magistrates were gifts from Berlusconi, according to the leaks.

(Additional reporting by Barry Moody; Editing by Tim Pearce)

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