Superstar Rihanna has provoked controversy after using the N-word to refer to a toddler on Twitter.

The 25-year-old singer was urged by fans to stop using the derogatory term after she captioned a snap of her holding a young boy "My lil nigga". Who the boy is has not been revealed.

RiRi, who recently resumed her Diamonds tour after cancelling a number of dates because of illness, found herself at the centre of a race row after tweeting the image taken on her recent holiday.

In one snap, the Barbadian songstress shows her maternal side by lifting up a toddler and cradling him in her arms.

"Playin hard to get, but he loves me!" she tweeted her 29.3 million followers.

Just days earlier, she upset fans by using the word while partying with friends. "It's the weekend and I am creeping with my niggaz," she wrote.

Fans flocked online to express their disapproval.

"The word is derogatory. If some cultures aren't allowed to say it, no-one should," one critic wrote.

Another said: "What happened to Rihanna? She is a loud foulmouthed horror who needs a good kick up the @rs."

Rihanna's controversial tweets come just months after she blasted a Dutch fashion magazine, Jackie, for calling her a "nigger bitch" in an article.

Jackie issued a public apology after she accused the publishers of racism.