Rihanna has been blasted by Twitter users after posting a four-letter rant on the social networking site.

The What's My Name singer, who reached over 3 million followers on the website yesterday, posted the rude four-letter word to one of her celebrity friends after he compared her to a cartoon dog on MTV.

US rapper KATT tweeted RiRi saying: "Watchin clifford the big red dog =) somehow im reminded of @Rihanna idk (I don't know) why tho."

The Rude Boy hitmaker responded with a foul-mouthed outburst, posting on her official Twitter page: "LMAO (Laughing my a*** off), Katt u lil c***."

According to The Sun, Rihanna's reply caused outrage amongst some of her fans, with one of the Barbadian beauty's followers stating: "Rihanna is a role model to millions of young, impressionable kids."