Maltese referee Terry Camilleri is at the centre of a snooker controversy after allowing a player to place his chalk on the table to line up a shot during a quarter-final match at the world championships being held in Sheffield.

Ronnie O'Sullivan broke snooker rules on Tuesday by lining up a shot with the chalk but was not reprimanded by the referee during his match against Stuart Bingham.

A World Snooker spokesman told BBC Sport it will look into the incident.

Although O'Sullivan was allowed to finish his break in the fifth frame, he went on to lose the next three as Bingham opened up a 5-3 lead after the first session. The match continues Wednesday afternoon.

Referee Terry Camilleri should have called a foul when O'Sullivan placed his chalk on the table to line up a shot, as snooker rules state a seven-point penalty will be awarded to the opponent if a player 'uses any object to measure gaps or distance'.

BBC pundit and former world champion Ken Doherty said: "As far as I am aware, you are not allowed to put the chalk on the table because you are using it as a tool to measure the ball.

"That is exactly what Ronnie has done. Stuart Bingham was looking at him and should really be aware. If he had more knowledge of the rules, he would have jumped up out of his chair."

It is not O'Sullivan's first controversy of at the Crucible in this championship.

He escaped a fine after briefly playing in his socks in his first-round win over qualifier Craig Steadman. He also came close to snapping his cue during his second-round match against Matthew Stevens.