FRENCH prosecutors today opened a preliminary investigation into accusations that disgraced ex-IMF chief Dominique Strauss-Kahn took part in a gang rape in the United States.

Prosecutors in Lille, where Strauss-Kahn and three others have been charged in a pimping case, said the probe centred on an incident “that could be described as gang rape” that took place in Washington, DC in December 2010.

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

Earlier this month Lille prosecutors said investigating magistrates in the case had submitted new evidence, based on testimony from two Belgian sex workers, that could also implicate the men in a gang rape.

Testimony from one of the prostitutes indicated that she had been forced into a non-consensual sex act while in Washington with Strauss-Kahn and the other accused. She has not filed a complaint.

In a statement from his lawyers this month Strauss-Kahn denied the accusations, saying he “absolutely contests having committed the slightest act of violence of any nature whatsoever.”

The former head of the International Monetary Fund and frontrunner for the French presidency, Strauss-Kahn suffered a stunning fall from grace following his arrest last year on accusations he sexually assaulted a New York hotel maid.

The charges were eventually dropped but Strauss-Kahn, 63, has since faced a series of criminal and civil actions in connection with alleged sex crimes.

The hotel maid, Nafissatou Diallo, has launched a civil suit against Strauss-Kahn in New York seeking unspecified damages, while he has in turn filed a $1 million countersuit for malicious prosecution and defamation.

The pimping case in Lille centres on accusations that prostitutes were procured for sex parties attended by Strauss-Kahn and paid for by executives who corruptly charged the parties to company expenses.

Strauss-Kahn admits he attended a string of orgies in various cities, but insists he had no idea that many of the female guests were paid to attend, telling police in a reported interview that he may have been “naive”.

After he resigned from the IMF and returned to France, Strauss-Kahn also faced an accusation from 32-year-old author Tristane Banon that he had tried to rape her in 2002.

French investigating magistrates questioned Strauss-Kahn and his accuser and concluded that, while there was prima facie evidence of a sexual assault, the alleged attack had occurred too long ago to be prosecuted.

Strauss-Kahn, a long-time Socialist Party member and former finance minister, had been the frontrunner to run for the party against incumbent right-winger Nicolas Sarkozy in France’s presidential election this year.

Following Strauss-Kahn’s legal troubles, former Socialist leader Francois Hollande emerged as the party’s candidate and defeated Sarkozy in the run-off vote on May 6.