Justin Bieber has been branded "disgraceful" by anti-racism campaigners following the publication of a video showing the troubled star singing about joining notorious hate group the Ku Klux Klan.

In the controversial clip, believed to have been filmed five years ago, the pop singer changes the words to his tracks One Less Lonely Girl to One Less Lonely N**ger, and sings about killing and the Kkk.

He has since apologised for letting down his legion of young fans, but the scandal has infuriated equal rights activists, who have branded the Baby hitmaker's behaviour "unacceptable".

Vince Maple, spokesman for U.K. campaign group Love Music Hate Racism, tells Britain's The Sun newspaper, "Someone of Justin Bieber's international fame making such inappropriate comments is unacceptable. He is idolised by millions worldwide and making such disgraceful comments has no place in the 21st century."

A representative for The Ramadhan Foundation, a group which works to promote tolerance among young people, adds, "We're appalled by it (Bieber's behaviour). It is unacceptable, particularly for someone in his position and with his influence."

The video was released just days after the publication of a similar clip which showed the star telling a racist joke and using the N-word. Bieber also apologised for that video, branding it a "reckless and immature mistake".