LILLE, France (Reuters) - French prosecutors said on Monday they had opened an inquiry into allegations of group rape by Dominique Strauss-Kahn and three friends, as part of an investigation into his ties to a suspected prostitution ring in the northern city of Lille.
The former IMF chief is under formal investigation over whether he was aware he was dealing with prostitutes and pimps when attending sex parties in Lille, Paris and Washington in 2010 and 2011 that were organized by business acquaintances.
Investigators asked prosecutors to extend the inquiry after a prostitute told them in her deposition that Strauss-Kahn and friends forced her to have sex in a group when she came to Washington to meet him in December 2010.
The woman has not filed a formal complaint.
"Following accusations by investigators... relating to events in Washington between December 15 and 18, 2010 that they believe could be qualified as group rape, Lille Prosecutors have ordered the start of a preliminary inquiry," the prosecutors said in a statement.
The case, dubbed the "Carlton affair" after the high-class hotel where the prostitution ring is alleged to have operated, is the latest scandal to rock Strauss-Kahn, whose career as a high-flying economist and Socialist politician was shattered last year by a separate sexual encounter.
Once tipped to win France's 2012 presidential race, he was forced to abandon his political plans and step down as head of the International Monetary Fund after being arrested in New York last May on charges of attempting to rape hotel maid Nafissatou Diallo.
Strauss-Kahn has always insisted the encounter was consensual and the charges were later dropped amid doubts over his accuser's credibility.
But the case was quickly followed by the emergence of the Carlton affair, casting a spotlight on the former finance minister's private life and opening the door to speculation about his apparently libertine ways.
Strauss-Kahn was placed under formal investigation in March in the Lille case, which had already led to the arrest of eight people including two Lille businessmen and a police commissioner.
He also faces a civil lawsuit in New York brought by Diallo, whom he is countersuing on the grounds that her accusations cost him his job and any chance of being elected president.
(Reporting By Pierre Savary in Lille; Writing by Vicky Buffery; Editing by Tim Pearce)