In legal terms, this is considered as procuring and is punishable by up to 10 years in prison.

Strauss-Kahn steadfastly denies knowing that the women with whom he engaged in "free and friendly" orgies were prostitutes, saying paying for sex would be too great a risk for a man at the head of the IMF, which was busy "saving the world from an unprecedented" financial crisis.

Tears and tension marked the start of proceedings Tuesday as an ex-prostitute, Jade, detailed a night in a Brussels hotel where she said Strauss-Kahn sodomised her without permission in what she said was a clear sign he knew she was paid to be there.

Jade sobbed as the court pushed her to recount the evening.

"I experienced a penetration without my permission. If I was a libertine, I would at least have been asked if I wanted to do that," she said, adding she had not had time to protest.

Strauss-Kahn said he did not know she objected and was "sorry" she experienced it that way.

The judge then asked Jade why she had agreed to a trip to Washington with Strauss-Kahn in January 2010.

"For 2,000 euros! I am not going to say no. I love travelling. I had never seen Washington," she said, admitting she had taken photographs of herself with Strauss-Kahn in his office at the IMF head office.

Jade said that while Strauss-Kahn's entourage had asked her to be "discreet" and pretend she was a secretary on the trip to Washington, she had previously had a conversation with him in which she mentioned she worked at a swingers club.

"He said 'it would be nice to come and see you one day'." Strauss-Kahn then took the stand and said being an erotic dancer did not make someone a prostitute.

Both Jade and another former prostitute have argued Strauss-Kahn would have been "naive" not to know they were paid.

Strauss-Kahn also rejected Jade's use of the word "carnage" to describe an orgy at a Belgian swingers club called Tantra, saying there were "dozens" of women there purely for the pleasure, who were not paid.

FOUR ORGIES A YEAR

Strauss-Kahn said Tuesday that as an unabashed libertine, the fun for him lay in the "playful party atmosphere" and that the presence of prostitutes would render such soirees seedy.

"I am horrified at the practise of using prostitutes," he said.

Strauss-Kahn also objected to the impression given by the prosecution of a "frenetic" schedule of sex parties, saying he only took part in such "recreational outlets" four times a year between 2008 and 2011.

"It has happened 10 times that a woman offers herself to me. It is nothing unusual to me," Strauss-Kahn said.

'RIGHT TO A PRIVATE LIFE'

Known in France as DSK, Strauss-Kahn finds himself back in the dock four years after his high-flying career and presidential prospects were torpedoed when he was accused of sexual assault by a New York hotel maid, a case later settled in a civil suit.

The trial breaks with France's traditional reluctance to peek behind the bedroom door of public figures.

"Everyone has the right to a private life," said Strauss-Kahn, the most high-profile of the accused who include a colourful cast of characters, including police, a prostitute, a lawyer and a notorious brothel owner known as "Dodo the Pimp." Strauss-Kahn's only female lawyer in his defence trio has been tasked with cross-examining the former prostitutes.

Frederique Baulieu on Tuesday presented evidence from a girlfriend who accompanied Strauss-Kahn to a party and described it as "free and friendly" - prompting judge Bernard Lemaire to say "this shows people have different views of libertinism".

Also questioned were members of Strauss-Kahn's entourage accused of organising and financing the parties.

Businessman Fabrice Paszkowski said he never told the former IMF chief he had paid the women to attend, as he would have been ashamed to do so.