The actor was taken from the Bristol Hotel, close to the Elysee Palace, where he was staying during the shooting of a film in Paris. Police sources refused to say why they thought that de Niro could help with the inquiry. They stressed that he had not been arrested.
Five people have already been placed under formal investigation in a 15-month inquiry which has revealed a call-girl network with tentacles around the globe. The clientele is reported to include Saudi princes and other Gulf potentates.
Several witnesses gave details last year of the brokering of a $1m sexual encounter in the South of France between an unidentified American actress and a member of a Gulf royal family.
The French government originally placed a brake on the investigation, apparently for fear of harming sales of arms to the Middle East. But the Socialist government which took power last June has freed the inquiry from these shackles.
The investigation led to the arrest in January last year of a Swedish former model, Annika Brumark, the apparent head of the network. Other arrests included a photographer, Jean-Pierre Bourgeois, and a Lebanese businessman called Nazihabdulatis Al Ladki.
Investigators seized diaries, records and address books. Mr Al Ladki also revealed the names of other alleged clients, including Saudi princes. Several witnesses spoke of the arrangement of a rendezvous at a palace in the South of France between a Gulf prince and an American actress, who was paid $1m for her services. Rumours of such a meeting had circulated for years but they are now being taken seriously by the French police.Reuse content