A French prosecutor has asked a criminal court to acquit Dominique Strauss-Kahn, the former International Monetary Fund (IMF) chief, of pimping charges for his alleged role in a sex ring involving prostitutes.

Strauss-Kahn, 65, was tipped to become French president before being accused of sexual assault by a New York hotel chambermaid in 2011. US criminal charges were subsequently dropped, and the allegations that he participated in a French sex ring centred in the northern French city of Lille emerged later.

"Did Dominique Strauss-Kahn pay prostitutes? The answer is no. Did he pimp prostitutes for others? The answer is no," Prosecutor Frederic Fevre told the court in the city of Lille before requesting Strauss-Kahn's acquittal.

"Our legal system must take pride in never convicting someone if there is any doubt. I therefore request his acquittal, pure and simple," said Fevre.

The prosecution's demand highlighted the difficulty of a potential conviction of Strauss-Kahn. The trial is due to finish this week, with closing statements from the defence on Wednesday, but a verdict is not expected immediately.

Investigating magistrates, who originally sent the case against Strauss-Kahn to trial over the objections of the same prosecutor, argued that the prominent Socialist was the instigator of parties involving prostitutes from 2008 to 2011 in Lille, Brussels, Paris and Washington.

Under French law, investigating magistrates have the right to overrule prosecutors' initial recommendations to drop a case.

The charge of pimping, or "procuring with aggravating circumstances", was justified, magistrates said, because Strauss-Kahn took a principal role in planning the parties, and knew that the women who attended them were prostitutes.

Plaintiffs drop claims of damages 

Earlier, lawyers for the four prostitutes who participated in sex parties organised for the ex-IMF chief gave up their claim of damages, saying it would be too hard to prove the pimping charge against him.

The four women remains civil parties in the criminal case, lawyers said.

Strauss-Kahn has steadfastly denied knowing that any of the women involved in the sex parties were paid.

Former prostitutes have given evidence against him, including one woman known as Jade who told the court she was taken by Strauss-Kahn to visit the IMF headquarters in Washington in January 2010.

In contrast, ex-IMF chief argued in court last week that the visit proves he did not think she was a prostitute, and that he was too busy "saving the world from an unprecedented" financial crisis to risk taking a call-girl to his workplace.

However, Jade also said he subjected her to a level of sexual degradation that he would only expect from a prostitute.

If convicted, Strauss-Kahn faces 10 years in prison and a fine of up to 1.5m euros ($1.70m).

Source: Agencies