Madonna has shared a nude photo with her Instagram followers in an attack on the image sharing site's censorship rules.
The superstar, whose 13th album Rebel Heart entered the British chart at number two last month, captioned the vintage picture: "Why is it ok to show ass but not breasts? Drowning in the hypocrisy of social media."
She added the hashtags #artforfreedom and #unapologeticb**ch.
Last year she fell foul of the site's obscenity rules after posting a picture from her 56th birthday showing a topless friend.
The image was removed, so the star posted a replacement image with the caption: "Instagram can take away our nipples but they can't take away our fun!"
<blockquote class="instagram-media" data-instgrm-version="4"><div><div><div /></div><a rel="nofollow" href="https://instagram.com/p/1AIRuXmEYY/" target="_blank" class="body-link" data-vars-item-name="BL-71776-https://instagram.com/p/1AIRuXmEYY/" data-vars-event-id="c23">Why is it ok to show ass but not breasts? Drowning in the hypocrisy of social media #artforfreedom #UnapologeticbItch ❤️#rebelheart</a>A photo posted by Madonna (@madonna) on <time datetime="2015-04-03T06:03:14+00:00">Apr 2, 2015 at 11:03pm PDT</time></div>
Instagram's terms of use state users "may not post violent, nude, partially nude, discriminatory, unlawful, infringing, hateful, pornographic or sexually suggestive photos or other content via the service".
Despite the 56-year-old's assertion, the website - which had more than 300 million active users at the end of last year - has in the past sparked controversy by deleting photos showing bare buttocks.
Madonna's post has so far been "liked" by more than 60,000 people.
The singer hit headlines following this year's Brit Awards, when she fell off the stage during a performance.
