NEW YORK — Ex-IMF chief Dominique Strauss-Kahn returns to a Manhattan court Friday for an unexpected appearance in the case on charges he attempted to rape a New York hotel maid, officials said.

"No details about this appearance will be available until the defendant appears in court tomorrow," said the statement from the Manhattan District Attorney's office Thursday.

No others details on the appearance were available, said the statement.

The former French finance minister had not been expected back in court until July 18.

Earlier Thursday, French newspaper Liberation, citing Strauss-Kahn's defense lawyers, said he was likely to challenge the legality of the identification line-up that took place a day after his May 14 arrest, where the then-IMF director had been picked out by the alleged victim.

Legal experts noted Thursday that a procedural error in the case would be difficult to prove, but could strengthen the defense argument that police had made errors in the hours after his arrest.

"It looks like one of the things they might raise at a preliminary hearing," Alexander Reinert, a law professor at New York's Yeshiva University, told AFP.

"It's going to be a stretch, legally. But it might throw out some of the evidence, and it could undermine the case."

Strauss-Kahn, a French national, has denied all seven charges including trying to rape the woman and sexually assaulting her when she came to clean his hotel suite in a luxury Manhattan hotel. He has been awaiting trial under house arrest.