Madonna who posted photos on her Facebook account of various celebrities with black strings on it has not gone down too well on social media.

She stirred up controversy especially after Mandela's picture was altered to look like her own image on her new album. Her Facebook post shows Nelson Mandela's face with strings to promote her new album 'Rebel Heart'. Some people considered these posts highly offensive.

Pop star Madonna has apologised for posting altered photographs.

She said, "I'm sorry. I'm not comparing myself to anyone. I'm admiring and acknowledging their Rebel Hearts. This is neither a crime or an insult or racist! I also did it with Michael Jackson and Frida Khalo and Marilyn Monroe. Am I saying I am them, No. I'm saying they are Rebel Hearts too.

And I didn't do it, my fans did. And I just re-posted those photos. My fans aren't racist either. If they put me in the same category as these other people, Thank You. I'm very flattered and I hope one day to live up to 1/100th of what those people accomplished."

The 56-year-old's cover for the album 'Rebel Heart' is a close-up of her face with black string on it.

Her social media posts show the faces of Princes Diana and Mr Mandela doctored to make it appear as though they have similar string on their faces. Some people considered these posts offensive.