Christina Aguilera's hits include Beautiful and Dirrty

David Keeler said he was attacked outside a nightclub in Hollywood as he tried to take the singer's picture.

"Christina has no reason to believe that such an incident did occur, nor did she witness such an incident," said a spokeswoman for Aguilera.

Mr Keeler is seeking damages from Aguilera and bodyguard Vernon Warren.

The legal action, filed at Los Angeles Superior Court, claims the alleged incident occured on 21 May, 2001 as Aguilera was leaving a club in the early hours.

Mr Keeler claims Aguilera "appeared to be intoxicated and needed assistance walking to the car".

'Physical force'

As he tried to take a photograph, he says Mr Warren told him he "needed to learn respect" and punched him in the mouth, leaving him "dazed, in pain and bloodied".

Mr Keeler alleges that Mr Warren was encouraged to "harass, intimidate, assault and batter photographers taking what defendants deemed to be photographs unflattering to defendant Aguilera".

The suit claims those named "instructed and encouraged [Mr Warren] to utilise physical force, regardless of whether it was warranted, while acting in the course and scope of his employment".