U2's new album is expected to be released in November

Police in Nice, in the south of France, said the band had made statements about a possible theft after the shoot at a recording studio in the city.

About 20 people are being questioned about the material's disappearance at the Victorine studios on Tuesday.

The album, which has not yet been named, is due for release in November.

Web specialist

Singer Bono, who has a house on the Cote d'Azur, and his fellow band members went to the police headquarters in Nice on Wednesday.

A police spokesman said: "We have to be careful. Was it lost or was it stolen? An inquiry is under way.

"We have numerous theories - from the fan who wants the rough cut for his collection to the web specialist who wants to be the first to put it out."

The rough cut does not have any great financial value but could be published on the internet in advance of the official release date, he said.

U2's latest album, All That You Can't Leave Behind, was voted fourth in a survey of the best albums of the past 10 years released earlier this month.