Lawyers for the four prostitutes who participated in sex parties organized for Dominique Strauss-Kahn said Monday they were giving up their claim of damages, saying it would be too hard to prove the pimping charge against the former IMF head.

Strauss-Kahn, 65, is accused of instigating parties he knew involved prostitutes between 2008-2011 in the French city of Lille as well as in Brussels, Paris and Washington.

The announcement was a surprise move on the first day of the final week of trial and suggests that Strauss-Kahn's defense — that he had no idea that the women at the parties were prostitutes — may have been effective.

The case will nevertheless continue against Strauss-Kahn and 13 other defendants, and the women will remain civil parties in the criminal case, said Gerald Laporte, the women's lawyer.

Strauss-Kahn is charged with pimping, or "procuring with aggravating circumstances," because investigating magistrates say he took a principal role in planning the parties, and that he knew the women who attended them were prostitutes.

"The prostitutes have renounced the request of damages and interest against Dominique Strauss-Kahn, reckoning that all the elements making up the crime of aggravated procuring have not been met," Laporte said.

Strauss-Kahn, Laporte said, "didn't give up" during questioning by judges, repeatedly denying knowledge that the women were prostitutes.

Strauss-Kahn was tipped to become French president before being accused of sexual assault by a New York hotel chambermaid in 2011. U.S. criminal charges were subsequently dropped, and the allegations that he participated in a French sex ring centered in the northern French city of Lille emerged later.

If convicted, Strauss-Kahn faces 10 years in prison and a fine of up to €1.5 million ($1.7 million).