Justin Bieber reportedly punched The Wanted's Siva Kaneswaran twice in the groin as a prank.

The British boyband were hanging out backstage at The Voice in Los Angeles after performing new single 'Chasing the Sun'.

Bieber is said to have walked up to the singer and jokingly smacked him twice.

"Justin Bieber is a prankster," Jay McGuiness told The Mirror. "He pranks people all day. Although I'm not actually sure that what he did to Siva was a prank.

"We'd done the show and Justin basically just came up and punched Siva hard in the balls. And then did it again. Siva wanted to hit him back, but you can't go around smacking kids… he's only little."

Kaneswaran confirmed the reports on ITV1 breakfast show Daybreak, saying: "He came up to me during a conversation and smacked me in the privates. It was a game, a very aggressive game, which was very painful!"

Tom Parker added: "Siva limped into the dressing room and asked 'Why's he picking on me?' It was funny."

Kaneswaran jokingly added that he is planning his revenge on Bieber, saying: "Who'd win in a fight, me or Bieber? Exactly. But you cannot go around hitting children. And anyway, he's got million-dollar sperm… I couldn't possibly go there. But I'll get him back..."

The Wanted are rumoured to be planning a duet with Bieber and Chris Brown in the near future.