Adverts by clothing company American Apparel have been banned by the Advertising Standards Authority (ASA) for having the "potential to normalise predatory sexual behaviour" towards young women.

The ASA said the images linked to the firm's 'School Days' and 'Back to School' ranges, one of which showed a women in a short skirt bending over so that her underwear was visible, amounted to "underage porn". The image is on the brand's website and Instagram page.

The advertising watchdog said the images were edited so "the focus was on her buttocks and groin rather than on the skirt being modelled".

The ASA said the adverts were "gratuitous and objectified women" and were "therefore sexist and likely to cause serious and widespread offence". They added that the adverts imitated voyeuristic "up-skirt" photographs taken without consent.

The ASA ruled: "We considered the ads had the effect of inappropriately sexualising school-age girls and were therefore offensive and irresponsible.

"We considered the ads had therefore not been prepared with a sense of responsibility to consumers or to society."

The images first appeared a month ago, prompting outrage among social media users.

In response to the complaints, American Apparel said the campaigns were "not graphic, explicit or pornographic but designed to show a range of different images of people who were natural, not posed and real."

The company said one of the models in the adverts was 30 and was one of the photographers, denying any intention to represent an underage model or be linked to a 'Back to School' marketing campaign.

This is not the first time the ASA has reprimanded the clothing retailer. In December 2013, the watchdog said images on the company's website gave the "impression that the women were vulnerable and in sexually provocative poses". In April 2012, the ASA said adverts run in Vice magazine appeared to sexualise a child.

The news comes just months after the suspension of the company's founder and chief executive Dov Charney, who was voted out by the retailer's board in June.

According to CNN, however, Charney was entitled to stay on as a "consultant" and receive his full base salary. American Apparel's website stated he oversaw the majority of the company's "creative content", which includes adverts.

Charney served as CEO and chairman of the board from December 2007 until this year, when he was removed from both roles. He faced numerous allegations of sexual misconduct including a claim that he received oral sex while being interviewed by a reporter.

In 2010, American Apparel was sued for allegedly terminating an employee who was undergoing cancer treatment.