Rihanna posts topless pictures on Instagram

R&B star Rihanna has posted a series of topless pictures on Instagram while vacationing in Brazil.

In the racy pics, Rihanna, 25, wears a gold string bikini and in some shots she has discarded the top, reported E! online.

The 'Diamonds' hitmaker had also uploaded photographs of herself cavorting in a botanical garden over the last weekend in a revealing one-piece.

Rihanna is currently in the South American state for a Vogue Brazil cover shoot.