Rihanna has come under fire after posting a picture online of herself with a white powder.

In a photograph the S&M star shared on Instagram, 24-year-old Rihanna is seen sitting on a man's shoulders appearing to "cut up" an unidentified powdery substance on top of his shaved head.

See the pic below:

The image, which was taken at last weekend's Coachella festival and seems to have been deleted, has caused outrage among web users – with some suggesting that she was rolling a joint and others were speculating that the star was readying cocaine.

Over 1000 comments were posted, with one users writing: "Yep take coke! U gonna die," while another added, "Chick looks like a druggie."

One users also compared Rihanna to the late Whitney Houston, writing: "I love her music, not her lifestyle. Hope she gets this under control before we have her funeral on TV like Whitney Houston."
Yet another wrote: "I have a ten-year-old daughter who loves her, and I wouldn't want my child seeing this."

In the past, Rihanna has insisted that she does not want to be seen as a role model.