The advertising watchdog has defended its banning of a Calvin Klein poster depicting British singer FKA twigs for presenting her as a “stereotypical sexual object” after the artist hit out at the ruling’s “double standards”.

The poster featured the 36-year-old wearing a denim shirt that was drawn halfway around her body, leaving the side of her buttocks and half of one breast exposed, with text reading: “Calvins or nothing.”

The Advertising Standards Authority (ASA) received two complaints that the images used were “overly sexualised”, offensive and irresponsible because they objectified women and were inappropriately displayed.

The artist, whose real name is Tahliah Debrett Barnett, challenged the complaints in an Instagram post on Thursday and thanked Calvin Klein for giving her the “space to express myself exactly how I wanted to”.

Alongside a picture of the poster, she wrote: “I do not see the ‘stereotypical sexual object’ that they have labelled me.

“I see a beautiful strong woman of colour whose incredible body has overcome more pain than you can imagine.

“In light of reviewing other campaigns past and current of this nature, I can’t help but feel there are some double standards here.

“So to be clear… I am proud of my physicality and hold the art I create with my vessel to the standards of women like Josephine Baker, Eartha Kitt and Grace Jones who broke down barriers of what it looks like to be empowered and harness a unique embodied sensuality.

“Thank you to CK and Mert and Marcus who gave me a space to express myself exactly how I wanted to – I will not have my narrative changed.”

Calvin Klein also previously defended the ad, saying it was similar to those it had been releasing in the UK for many years.

The fashion brand said FKA twigs, who it described as a “confident and empowered woman”, had collaborated with Calvin Klein to produce the image and had approved it before publication.

It added that all “conventionally sensitive” body areas were fully covered and the subject was in a natural and neutral position.

The Advertising Standards Authority’s director of complaints and investigations, Miles Lockwood, said the watchdog finds itself “damned if we do, damned if we don’t” in such situations, saying: “This is a clunking great big poster on the street in an untargeted medium. Children are seeing it alongside adults, and sometimes that gets missed.”

Mr Lockwood said the decision to ban the ad, and not to uphold complaints about two posters from the same campaign featuring model Kendal Jenner topless with her hands across her bare chest and lying on her back wearing underwear and pulling down a pair of jeans past her hips, was made by the ASA’s council of 12 members, “two-thirds who are not from an advertising background, and a range of genders, ages, backgrounds and ethnicities”.

In its ruling, the ASA said the poster featuring FKA twigs used nudity and centred on her physical features rather than the clothing – a denim shirt – to the extent that it presented her as a stereotypical sexual object.

Explaining its decision not to ban the poster featuring Jenner lying on her back, it said that, while the model was partially nude, all sensitive body areas were covered and the image was no more than “mildly sexual”.

The watchdog said the poster of her wearing a bra and pants with the slogan “Calvins or nothing” placed across her upper thigh and hip had the effect of drawing the viewer’s attention to her crotch, and combined with her “sultry expression” made it “sexually suggestive”.

The ASA noted that all three posters were restricted from appearing within 100 metres of schools.

Mr Lockwood said: “This case went to the December meeting, where they held long discussions and considered similar cases concerning sexual objectification – both upheld and not upheld – to make sure they were in line with other decisions.

“Inevitably with this sort of judgment, they are subjective at the end of the day, and we have to make a decision.

“We are balancing the right of the advertiser’s freedom of expression with protecting the public from offence and harm, and that’s the process we go through every week.”

Mr Lockwood also said the ASA does not “play a numbers game” when it comes to complaints, and that the two received from members of the public in this case were as valid as receiving hundreds for a single ad.

“If we played a numbers game that would lead to some really illogical outcomes. Sometimes a single complaint can raise incredibly important issues.”