Supermodel Irina Shayk has sparked outrage by posting a topless picture of herself as part of a campaign calling for the return of the Nigerian schoolgirls kidnapped by Islamist militants.

Public figures including U.S. First Lady Michelle Obama, Hillary Clinton, Anne Hathaway and Angelina Jolie have all spoken out about the hundreds of teenagers snatched from a school in northern Nigeria last month (Apr14) by members of the Boko Haram extremist group.

They have backed a Twitter campaign called #BringBackOurGirls, which encourages supporters to post a photo with a sign emblazoned with the hashtag, and Shayk uploaded her own snap on earlier this week (beg12May14).

However, her involvement has prompted criticism as she appears to be topless in the photo, with her '#BringBackOurGirls' sign covering her breasts.

Many followers took to to share their disapproval of the post, with users branding the image "callous" and "self-centred", but Shayk is refusing to take notice.

She subsequently uploaded a photo featuring the saying: "A tiger doesn't lose sleep over the opinion of sheep."