Bosses of a British disability charity are urging Kanye West to avoid the word 'spaz' in future raps after he sparked outrage by using the offensive term in his track with Rihanna and Sir Paul McCartney.

The Stronger hitmaker raps the line, "Then I heard you was talkin' trash/ Hold me back I'm 'bout to spaz" during his verse in Rihanna's latest single Four Five Seconds, which also features MCCartney.

The lyric has angered critics, and Richard Hawkes, the chief executive of U.K. charity Scope, wants the rapper to watch his words in future.

Hawkes tells British newspaper The Sun, "Many disabled people find the word 'spaz' very offensive... Kanye West is a huge star, listened to by millions of young people who might be influenced by his songs.

"It would be such a shame if the world became commonplace again. We've contacted Kanye and asked him not to use this word in future recordings."