(CNN) -- French prosecutors have widened an investigation into former International Monetary Fund chief Dominique Strauss-Kahn's alleged participation in a prostitution ring.
Authorities said Monday that Lille police will open a preliminary inquiry into acts that allegedly took place in Washington, which they believe could constitute gang rape.
"Following the decision by the examining magistrates, who are in charge of the affair known as the 'Carlton affair,' they have reason to believe ... pertaining to events which allegedly took place in Washington between December 15 and 18, 2010, that there is suspicion of gang rape," a statement from the Lille prosecutor's office said.
Strauss-Kahn's attorneys issued a statement saying, "The investigation will establish that Dominique Strauss-Kahn has never committed acts of violence or had any relationship whatsoever without the consent of his partners."
The French newspaper Liberation reported earlier this month that the allegations stemmed from statements made by two women it describes as "escort girls," who were interviewed by Belgian police as part of an investigation into a prostitution ring run out of the Carlton Hotel in Lille, near France's border with Belgium.
According to the newspaper's account of the depositions, the women said they had accompanied two associates of Strauss-Kahn on a visit to Washington, where they had stayed at the W Hotel.
One of them alleged that Strauss-Kahn had used force against her during a sexual encounter at the hotel, despite her protests.
The newspaper did not specify how it obtained the statements. CNN could not independently confirm the report.
The Metropolitan Police Department in Washington said no sexual assault at the hotel was reported at that time.
French law allows authorities to prosecute a French national for a crime committed abroad.
In a statement to Agence France Presse, Strauss-Kahn's attorneys Frédérique Baulieu, Richard Malka and Henri Leclerc said the "declarations made by these young women are contradictory." It also said the women's testimony was disclosed at an "opportune time," just before the final round of the French presidential election.
The prostitution investigation continues a string of sexual allegations against Strauss-Kahn. He has not been convicted of a crime.
Strauss-Kahn has been formally warned by French authorities that he is under investigation for "aggravated pimping" in connection with the prostitution investigation and has been released on 100,000-euro bail. He has pushed back against the accusations, saying he did not know young women at parties he attended were being paid for sex.
One of the sex scandals torpedoed his expected run for the French presidency this year. He stepped down from the top job at the International Monetary Fund after the May 2011 incident, in which a New York hotel maid accused him of sexual assault and attempted rape in May. He denied the accusation.
The case ultimately fell apart after prosecutors decided they could not be sure about the credibility of the alleged victim, despite forensic evidence that showed a sexual encounter had occurred.
The maid, Nafissatou Diallo, has since launched a civil action against the former IMF chief, alleging a "sadistic assault." This week a judge in New York rejected Strauss-Kahn's claim of diplomatic immunity.
Strauss-Kahn also faced allegations of attempted rape from a young French writer. Tristane Banon filed a complaint, alleging a 2003 attack, though it could not be pursued because of a statute of limitations.
He denied the allegations and has since filed a countersuit in France, alleging slander.
CNN's Tim Lister, Stephanie Halasz, Carol Cratty and Susan Candiotti contributed to this report.