The U.K.'s Advertising Standards Authority has banned two online ads for American Apparel's "back to school" range for sexualizing school girls.

The images, which appeared on the retailer's website and Instagram page, were judged irresponsible, harmful and offensive by the advertising watchdog. The website image showed a girl wearing a short skirt, bending over to touch the ground and exposing her underwear in the process. In the Instagram post, a girl wearing a very short school skirt is leaning into a car and photographed from behind, her underwear clearly visible.

Complaints to the ASA said the online ads -- created in-house -- were offensive because they were overtly sexual, and inappropriate for a skirt advertised as school-wear.

In its defense, American Apparel came up with a long list of excuses. The retailer said its approach was not graphic, explicit or pornographic, and was designed to show a range of people who were natural and real. The company also justified the ads by saying that models are not portrayed in a manner that was vulnerable or exploitative, and that the model was 30 years old.

More excuses were piled on: the images were posted by an inexperienced member of the social media team, and the clothing retailer said it draws a strong distinction between its advertising in print or other traditional media, and web or social media, where consumers opt to view the images.

The ASA, however, ruled that the ads were gratuitous, objectified women, and were likely to normalize predatory sexual behavior and cause widespread offense. The watchdog also rejected American Apparel's defense that the model was over 30, because her face isn't visible.

As well as banning the ads in question, the ASA warned American Apparel to "ensure its future advertising was prepared with a sense of responsibility to consumers and to society and contained nothing to cause serious or widespread offense."

The retailer has removed the images.