LONDON (Reuters) - Britain's advertising watchdog has criticized an ad for a clothing company featuring a partially nude model who appeared to be younger than 16.

The advert for American Apparel clothing featured on the back cover of Vice magazine, a free publication aimed at 18 to 34-year-olds, and showed the young-looking girl modeling a hoodie top in a series of photographs.

In one picture, she was wearing the hoodie unzipped and one of her nipples was partially exposed.

One reader complained to the Advertising Standards Authority (ASA) that the ad was offensive and inappropriate because the model appeared young and it could be seen to sexualize a child.

American Apparel said although the advert did feature partial nudity, it did not think it would cause widespread offence.

It said the model was 23 and did not look under 16, nor was she portrayed as a sex object.

However the ASA disagreed, and ruled that the advert should not be used again.

"While the ad depicted only partial nudity, we considered that the images were provocative with the model exposing progressively more skin in each photo in the series," the ASA said.

"Because the ad could be seen to sexualize a model who appeared to be a child, under the age of 16 years, we concluded that it was inappropriate and could cause serious offence to some readers."

(Reporting by Michael Holden; Editing by Steve Addison)