Prince recently performed for 21 nights at London's O2 arena

A fan group, Prince Fans United, claims the star is trying to "stifle all critical commentary" and he is in "violation of the freedom of speech".

But Web Sheriff, the UK firm the pop star has hired to enforce the ban, said it was "not an attack on fans".

In September, Prince took action against video sharing website YouTube to remove clips of his London concerts.

'Voluntary and unpaid'

He is now hoping to have any album covers, images of him in concert and any lyrics removed.

"The dispute, in so far as there is one, is related to the use of photographs and images of Prince, many of which are Prince's copyright," said John Giacobbi, managing director of Web Sheriff.

"At the end of the day it's the artist's decision as to what they're happy to let people have," he added.

However, a spokesman for Prince Fans United, who asked to remain anonymous for legal reasons, denied the sites had done anything wrong.

The websites are run by fans, therefore it is an attack on fans

Prince Fans United spokesman

"We respect copyright laws always. However about 80% of the images on the websites are not copyright owned by Prince," he said.

"For example there are photos taken of him in concert where the copyright remains with the photographer."

Tight security

Prince Fans United was formed by housequake.com, Princefams.com and Prince.org, to fight back.

The spokesman said all the websites were run on a "voluntary unpaid basis" and none of the sites were a "commercial venue".

He added: "The websites are run by fans, therefore it is an attack on fans."

During Prince's recent residency at London's O2 arena, fans were banned from taking photographs or video footage on their mobile phones.

Prince publicly protested against his record company in the 1990s

Security at the concerts was tight with people's bags being searched for cameras.

But clips of the singer still appeared online.

Prince is well-known for being protective of his image.

In 1990 he fell out with his record company, Warner Brothers, over the ownership of his master tapes.

He went on to change his name and famously wrote the word "slave" on his cheek during public appearances.

More recently, in the UK his most recent album, Planet Earth, was given away free with a newspaper.

Several websites offered copies of the album for download as soon as the paper went on sale - despite the album being sold commercially in the rest of the world.