Prime Minister Silvio Berlusconi on Monday accused Italy's judges of being out to get him and laughed off his ongoing sex crime trial as he returned to court on fraud charges in a separate trial.

"The prosecutors are working against the country," Berlusconi told reporters in the courtroom, as some 200 supporters outside held up placards reading 'Silvio Resist!' and clutched blue balloons from his People of Freedom party.

He said there should be an overhaul of Italy's justice system to prevent it becoming 'a weapon of political struggle' - after his government earlier this year proposed reforms seen as curbing the power of investigating magistrates.

The prime minister also condemned his trial on charges of sex with an underage prostitute and abuse of power which began last week.

The accusations were 'laughable, unfounded and crazy', he said.

Berlusconi admitted he had given money to the woman in question - then 17-year-old nightclub dancer Karima El Mahroug, better known as 'Ruby the Heart Stealer' - but said it was in order 'to allow her not to prostitute herself'.

"The girl told me and everyone else present her painful story and I was moved," Berlusconi said, adding that he had given her tens of thousands of euros (dollars) to allow her to buy equipment to set up a beauty salon.

Twice-divorced Berlusconi, 74, is accused of paying for sex on several occasions last year with El Mahroug and then abusing his status to get her released from police custody in a later incident to cover up his alleged crime.

The underage sex charge carries a maximum sentence of three years, while the abuse of power accusation is punishable by up to 12 years in prison.

He also repeated his assertion that he intervened in El Mahroug's arrest because he thought she was former Egyptian president Hosni Mubarak's niece.

"I have always been very polite and I asked for information out of concern for a situation that could have led to a diplomatic incident," he said.

After coming out of the hearing and greeting his supporters at a campaign-style rally outside the Milan courtroom, Berlusconi said the Mediaset hearing had been 'surreal' and again denied the fraud charges.

As his supporters applauded, Berlusconi said that the hearing was a waste of time and that he should be 'defending Italy on the international scene'.

In the Mediaset trial, Berlusconi and his co-defendants are accused of artificially inflating the price of distribution rights bought by his companies and of creating foreign slush funds to avoid paying taxes in Italy.

The trial was suspended in April 2010 after Berlusconi's majority in parliament adopted a temporary immunity law. The Constitutional Court partially struck down the law in January and the trial resumed on February 28.

The tycoon turned politician has a long history of legal woes dating back to when he first entered politics in the early 1990s but has always either been exonerated or seen his trials expire under a statute of limitations.

Last month, Berlusconi attended a court hearing for the first time in eight years for a separate fraud investigation linked to his company Mediatrade. Judges have not yet decided whether that case should go to trial.

Photographers and television crews have been banned from the Milan courtroom for cases involving the prime minister including the sex crime trial which began on Wednesday and another trial for bribing British lawyer David Mills.

The opposition Italy of Values party criticised Berlusconi's statements, saying he wanted 'to destroy the Italian justice system in order to ensure his immunity' particularly with a new draft law that would reduce trial times.