Former IMF chief Dominique Strauss-Khan is to face trial on pimping charges in relation to his involvement in a suspected prostitution ring that operated out of Lille's Hotel Carlton, according to French prosecutors.

Strauss Khan has always refuted accusations that four of his associates, including two businessmen, police commissioner Jean-Cristophe Lagarde and the son of a local politician, arranged 15 "bunga bunga-style" parties for his benefit in Paris, Lille, Belgium and Washington.

He said he did not know that the women, as young as 20, were being paid for sex.

Using prostitutes is not illegal in France but investigators suspect that the prostitutes with whom Strauss-Khan allegedly had sex were paid for using company funds.

The case was launched after DSK settled a separate civil case in New York with a hotel maid who accused him of attempted rape in May 2011, ending his presidential hopes and career at the IMF.