French investigators were due on Thursday to question Dominique Strauss-Kahn as part of their probe into allegations that the disgraced former IMF chief procured prostitutes for sex parties.

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The summons for interrogation in Lille, confirmed by legal sources, came after a court in the northern city in December rejected a request that the pimping charges against him be dismissed.

Strauss-Kahn last month agreed a financial settlement with a New York hotel maid who had accused him of sexual assault in a 2011 case that forced him to resign from his IMF job and wrecked his chances of becoming French president.

Strauss-Kahn admitted a sexual encounter took place but insisted it was consensual. A criminal investigation into the incident collapsed after the maid changed her version of events.

French prosecutors however are convinced they have a case against Strauss-Kahn for "aggravated pimping in an organised gang."

The case, known here as the "Carlton affair", centres around allegations that business leaders and police officials in Lille operated a vice ring supplying girls for sex parties, some of which are said to have taken place at the city's Carlton Hotel.

The Carlton case is one of a series of probes that were launched in the aftermath of Strauss-Kahn's arrest in New York.

French writer Tristane Banon accused him of trying to rape her in 2003. Investigators concluded that while there was evidence of sexual assault, the alleged attack had occurred too long ago to be prosecuted.

Strauss-Kahn was also investigated over an allegation that he had taken part in the gang rape of a Belgian prostitute. The case was dropped when she recanted and said she had consented to sex.