Two adverts by fashion brand Zara have been banned for featuring models who appeared “unhealthily thin”.

The Advertising Standards Authority (ASA) said shadows and a slick back bun hairstyle made one model appear “gaunt” while the pose and low cut design of a shirt in another image showed the model’s “protruding” collarbones.

The watchdog ruled that the “irresponsible” adverts must not appear again in their current form and that Zara must ensure all its images were “prepared responsibly.”

Zara has removed the adverts and said that both models in question had medical certification proving they were in good health when the pictures were taken.

The two banned adverts previously appeared on the retailer’s app and website in a carousel of images showing clothes on and off models.

One advert was for a short dress and the ASA felt shadows were used to make the models legs look “noticeably thin”.

It also said the positioning of her upper arms and elbow joints made her look “out of proportion.”

The other banned advert was for a shirt and the model was said to be in a position that made “protruding” collarbones a “focal feature” of the advert.

The ASA investigated two other Zara adverts but neither were banned.

Zara chose to remove all the images flagged and said it had not received any direct complaints.

The retailer told the ASA that none of the images had been modified beyond “very minor lighting and colouring edits”.

It added that it followed recommendations of a report called Fashioning a Healthy Future, which was published in 2007 by the UK Model Health Inquiry.

Zara said it specifically complied with recommendation three of that report which said models “should provide a medical certificate attesting their good health from doctors with expertise in recognising eating disorders.”

It comes after adverts by other retailers were banned earlier this year for models being too thin.

In July, an advert by Marks & Spencer was banned because the model appeared to be “unhealthily thin”.

The ASA said the pose of the model and the choice of clothing – including “large pointed shoes” which emphasised “the slenderness of her legs” – made the advert “irresponsible”.

Earlier this year, fellow retailer Next also had an advert for blue skinny jeans banned.

The ASA said the advert emphasised the thinness of the model’s legs using camera angles, and deemed it “irresponsible”.

Next said it disagreed with the advertising watchdog’s decision and said the model, while slim, had a “healthy and toned physique”.

The Next advert ban left BBC readers asking why adverts showing models who appear unhealthily overweight are not banned.