Strauss-Kahn, two businessmen and a police chief had already been charged with “aggravated pimping in an organised gang” for allegedly organising a prostitution ring for orgies in France, the United States and elsewhere.

On Friday, a spokesman for the state prosecutor’s office in the northern French city of Lille said that investigating magistrates had submitted new evidence that could also implicate the men in a gang rape.

“The Lille prosecutor was presented by the magistrates charged with investigating the ‘Carlton affair’ with a notice to make known, for whatever useful purpose, evidence of gang rape,” the spokesman said.

It was understood the magistrates have not requested they be permitted to formally investigate an alleged rape, but for official purposes have warned the prosecutor that some testimony points in that direction.

Following such a notice, a prosecutor can either throw out the allegation or order a preliminary inquiry to establish if there is enough prima facie evidence to expand the original probe to include the newer charge.

“This notice is being examined,” the prosecution spokesman said.

The notice is based on testimony from a Belgian sex worker who alleged she was forced to take part in sex acts against her will at a party attended by Strauss-Kahn and his friends in a Washington hotel suite in December 2010.

Another escort present at the party partially confirmed her statement, but neither has sought to press charges.

Strauss-Kahn has admitted he had a free-wheeling sexual lifestyle when he was managing director of the Washington-based International Monetary Fund, but he has fiercely denied that he was ever violent towards a partner.

Last May, Strauss-Kahn was arrested in New York after a hotel maid alleged he had subjected her to a brutal sexual assault in his hotel suite.  

The criminal case collapsed amid doubts about the alleged victim’s testimony, but she is still pursuing a civil suit against him, and on his return to France Strauss-Kahn found himself implicated in other scandals.

The so-called “Carlton affair” centres around allegations that business leaders and police officials in the northern city of Lille operated a vice ring supplying girls for sex parties, including at Lille’s Carlton Hotel. 

The same ring is alleged to have supplied women for orgies attended by Strauss-Kahn in Paris, Washington and European cities and investigators believe they can prove the former finance minister committed crimes.

Paying for sex is not illegal in France, but profiting from an organised vice ring is, and Strauss-Kahn – who until last year was seen as a likely future French president – could face a lengthy jail term.

Strauss-Kahn’s lawyers issued a statement on Friday in which they said their client denied committing any acts of violence against women.

Strauss-Kahn “absolutely contests having committed the slightest act of violence of any nature whatsoever,” the statement said.