Former IMF chief Dominique Strauss-Kahn was released from a French police station yesterday after two days of questioning about an alleged illegal prostitution ring.

The 62-year-old former Socialist minister was driven away by car under a police motorcycle escort from the station in the northern city of Lille.

Prosecutors said Strass-Kahn, once considered a front-runner to become the next French president, would be summoned to appear again before investigating magistrates next month over a series of sex parties.

During his interrogation, Strauss-Kahn told investigators he did not suspect the women he met at orgies were prostitutes as they were introduced to him by senior police officers, a source close to the investigation said.

Frederique Baulieu, one of Strauss-Kahn's lawyers, said his client was "perfectly satisfied" to have been heard by investigators and that he had responded to the questioning in a "calm" manner.