LILLE, FRANCE (Reuters) - Former IMF chief Dominique Strauss-Kahn was put under formal investigation by a French court on Monday over his role in a prostitution case, his lawyer said.

The move is an escalation of the case against the Socialist ex-finance minister but falls short of a formal charge.

Strauss-Kahn has denied the allegations against him, arguing that he was unaware women he met at parties organized by business associates in Lille, Paris and Washington were prostitutes.

(Reporting By Gerard Bon; Writing by Alexandria Sage; Editing by Karolina Tagaris)