Disgraced former International Monetary Fund boss Dominique Strauss-Kahn told a French court today that he was unaware that women who participated in orgies at luxury hotels in Paris and Washington DC were prostitutes.

65-year-old Strauss-Kahn and 13 co-defendants are on trial in this northern French city, accused of aggravated pimping in connection with a sex ring centred on the Hotel Carlton in Lille.

In his first testimony since the trial began 2 February, Strauss-Kahn reaffirmed his long-standing defence that he ignored the "prostitutional character" of the women who took part in his orgies.

Strauss-Kahn's arrival at the courthouse was disrupted by three topless protesters from the provocative group Femen, who were detained by police.

Strauss-Kahn's chances of becoming French president were ruined over an unrelated sex scandal in New York.

The economist, known widely as DSK, faces up to 10 years in prison and a €1.5 million fine if convicted.

Strauss-Kahn is on trial with 13 other defendants accused of operating a prostitution ring out of luxury hotels in Paris, Washington DC, Lille and Brussels.

The court has so far heard testimony from some of Strauss-Kahn's fellow defendants, who include a Belgian brothel owner, local businessmen, a police officer and hotel staff accused of organizing sex parties for Strauss-Kahn's benefit.

Investigators have compiled hundreds of pages of testimony from prostitutes describing the orgies.