French prosecutors have opened a preliminary investigation into rape allegations against former International Monetary Fund chief Dominique Strauss-Kahn.

Prosecutors in Lille said Monday Strauss-Kahn may have been involved in a rape during a sex party in December 2010 in a Washington hotel.

He is also facing charges in Lille in connection with a prostitution case.

Strauss-Kahn has denied the allegations against him and said he is not guilty of any violence.

A New York hotel maid accused Strauss-Kahn of sexually assaulting her last year in the luxury hotel where she worked. Those charges were dropped when prosecutors questioned the woman's credibility, but not before Strauss-Kahn was forced to step down as IMF chief.

Earlier this month, he counter-sued the maid, Guinea native Nafissatou Diallo, saying she cost him not only his IMF job but also political opportunities including the French presidency.

Diallo's lawyers called the $1 million lawsuit a publicity stunt.

Socialists had earlier touted Strauss-Kahn as a likely president candidate. Instead the party backed newly elected President Francois Hollande, who defeated former leader Nicolas Sarkozy in a runoff vote earlier this month.