PARIS – Former IMF head Dominique Strauss-Kahn is being questioned by French police as a suspect in a prostitution ring inquiry, a prosecutor says. Mr Strauss-Kahn, once a front-runner for the French presidency, is being held in custody at a police station in Lille, northern France, BBC informs. Police have questioned a number of prostitutes who have admitted having sex with Mr Strauss-Kahn.He insists he did not know that the women were prostitutes. “I challenge you to distinguish a naked prostitute from any other naked woman,” his lawyer Henri Leclerc has told French television. Mr Strauss-Kahn resigned as head of the International Monetary Fund (IMF) in May 2011 after he was charged in New York with the attempted rape of a hotel maid. The case was later dropped.In this separate inquiry, French police have already arrested eight men on suspicion of organising a prostitution ring and misusing corporate funds to pay for sex in a scandal known as the “Carlton affair” because of a Lille hotel where clients were allegedly supplied with call-girls. Three of the suspects were said to have been close to Mr Strauss-Kahn, who is said to have taken part in sex parties in Paris and Washington in late 2010 and early 2011.