Six reporters, photographers and media chiefs are to be tried in France for invasion of privacy over topless photos of Britain's Duchess of Cambridge published in 2012, judicial sources said Tuesday.

The snaps of Kate, the wife of Prince William, were taken with a long lens and showed her topless on a balcony of a private residence in the south of France during a holiday with her husband.

The photos, which first appeared in French celebrity magazine Closer in September 2012, sparking fury from the British royal family and reviving a debate on press intrusion into the private lives of celebrities.

Closer's chief editor, the head of the Mondadori press group which owns the magazine, two photographers of a Parisian agency and a photographer and a senior figure at regional daily La Provence will now have to answer in court over the publication of the intimate photos, under a July magistrate's order.

The pictures in question first appeared on the front page of the regional daily in southern France on September 7, 2012, before Closer gave them a wider audience a week later.

The directors of La Provence have denied that one of their photographers took the offending pictures.

The topless images were later published elsewhere in Europe, notably in Chi magazine, also owned by former Italian prime minister Silvio Berlusconi's Mondadori media group, as well as in Denmark, Ireland, Italy and Sweden.

The royal couple had lodged a complaint over the pictures.

The royal family's lawyers obtained a civil injunction and sought criminal charges in Paris in a bid to curb the spread of the pictures.

The pictures revived debate about invasions of privacy by the press and brought echoes of the hounding by paparazzi endured by William's mother, Princess Diana, who died in Paris in 1997 after the car she was in crashed while fleeing scooter-riding photographers.

The French trial for the Kate photos will be held some time next year.