LILLE, France (AFP) - A former prostitute detailed scenes of group sex as "carnage" at orgies with Dominique Strauss-Kahn on Tuesday, as the former International Monetary Fund chief said paying for sex would be too great a risk for a man who was busy "saving the world".

Strauss-Kahn took the stand for the first time on charges of "aggravated pimping" in an alleged vice ring, in a day of high drama in a French court.

The silver-haired economist once tipped for the French presidency denied having a "frenetic" programme of sex parties at a time when the IMF he headed up was "saving the world from an unprecedented" financial crisis, adding they only took place four times a year between 2008 and 2011.

Dressed in a dark suit, he told the court in the northern French city of Lille that he would never have attended the sex soirees in Paris, Brussels and Washington if he knew the women were paid to be there.

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

Strauss-Kahn admits being a libertine and said that while he accepted the risk of unusual sexual practices for a man of his stature, he would not have taken the risk of paying prostitutes who would be susceptible to "pressures".

The 65-year-old 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 crux of the case against him is whether he was aware the women were paid by members of his entourage and whether he played a role in organising the parties, which he also denied.

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

Asked to define a libertine party, he said it was when men and women "came together for the pleasure of sex" and what he liked was the "party atmosphere" of such soirees.

However one former prostitute, Jade - who attended several parties with DSK - described scenes of "carnage" at such a party at a chic Parisian hotel.

"There was (DSK) surrounded by women" on a bed. "That isn't libertinism, there were no other men. No one asked my name, there was just a hand on my head to perform fellatio," she said.

However Strauss-Kahn's female lawyer Frederique Baulieu read evidence from a girlfriend who accompanied him to the party and described it as "free and friendly" - prompting court judge Lemaire to say "this shows people have different views of libertinism".

Mounia, another former prostitute, also detailed how Strauss-Kahn performed a sexual act on her which was "against nature" during the party, despite her tears.

"I think he realised (I didn't want to do it)," she said, adding that she had not refused it because she needed the money.

Strauss-Kahn strongly denied this, saying her tears would have "chilled" him.

"What is sure is we didn't experience the same thing (at that party). To me it was friendly, playful."

Both Jade and Mounia said they had not mentioned to DSK that they were prostitutes.

And Strauss-Kahn's close friend, businessman Fabrice Paszkowski who is accused of financing and organising the parties, said he never told the former IMF chief he had paid the women to attend.

Prostitution is legal in France but procuring - the legal term for pimping which includes encouraging, benefiting from or organising prostitution - is a crime.

Strauss-Kahn is the most high-profile of the 14 accused with "aggravated pimping", some also with fraud, and his presence at the court drew crowds of journalists and curious onlookers.

He faces up to 10 years in jail if found guilty of aiding and abetting prostitution.

As he arrived at the court, topless Femen activists threw themselves on his car, one of them with "pimps, clients, guilty" scrawled across her chest.

He is in the dock with a colourful cast of characters in interlocking vice cases, including police, a prostitute, lawyer and notorious brothel owner known as "Dodo the Pimp".

The trial is the latest in a series of cases offering a peek behind the bedroom door of a man once tipped as a potential challenger to former French president Nicolas Sarkozy.

It also casts the spotlight on the separation of a man's public and private activity in a country where it has long been viewed that what public figures do is their own business.

"Everyone has the right to a private life," said Strauss-Kahn, who will have two more days to convince the court he was not at the core of a prostitution ring when the trial resumes Wednesday.