PARIS (AP) _ French investigators reportedly have cracked a ring that supplied prostitutes to the super-rich, and included liaisons at Riviera palaces and aboard yachts owned by Persian Gulf royalty.

Though few names have been made public, the widening probe is especially embarrassing for a French government that relies on its relationships with Gulf oil states that are major buyers of French military hardware.

A central figure in the probe is Paul Barril, a former deputy commander of the special forces National Gendarme Intervention Group, who was fired for alleged misconduct. He went on to form his own security agency, counting the former emir of Qatar among his clients.

Five people have been placed under formal investigation _ one step short of being charged _ since the case broke in February after a four-month probe that included telephone surveillance, the French daily Le Monde reported Tuesday.

One of them, Cannes doctor Alain Meyer, is being investigated for ``complicity with aggravated pimping'' for treating prostitutes presented to Arab princes, Le Monde said.

While prostitution is legal in France, pimping is not.

In his April 18 deposition, the doctor described visits to certain villas in Cannes and Paris as well as royal yachts, Le Monde said. Police found evidence he was an employee of a member of the Saudi royal family.

Former model Annika Brumark and Jean-Pierre Bourgeois, a photographer for the soft-porn magazines Lui and New Look, have been accused of receiving fees from young prostitutes.

The two, considered the architects of the ring, which charged between $500 and $8,600, have been in detention since January, Le Monde reported.

Also jailed under formal investigation are Nazihabdelatif Al Ladki, an alleged madam to Saudi royalty, and ``a large number of French and foreign personalities,'' the paper said.

Barril was released Tuesday afternoon after being held 24 hours for questioning, a police official said on customary anonymity. He was asked about depositions from two Morrocan prostitutes who said Barril had helped them enter the country, and about statements by a bodyguard who said he had seen young Morrocan call girls at an emir's Riviera villa.

The police official said Barril denied all the allegations and called himself a ``victim of a conspiracy.''

Police on Monday searched the offices of Barril's security agency, Secrets. They also visited the swanky Hotel Crillon on the Place de la Concorde, where the former emir of Qatar, Al Thani, employed Barril to coordinate his security. The emir's son, who assumed power in July 1995, also pays Barril for protection services.

Le Monde reported that Nazihabdelatif Al Ladki's address book, which was seized by police, contains hundreds of names and numbers from every continent. Clients and prostitutes came from Bosnia, the United States, Britain, Indonesia and Morocco, the paper said.

An unidentified American actress is rumored to have been paid $1 million to spend the night with a Gulf prince in a Riviera palace, Le Monde reported.