"We have to stop this type of behaviour," said UEFA Referees' Committee member Hugh Dallas on the UEFA's website.

"Confrontation now is becoming a bigger problem in our game. It's tactical, it's deliberate."

Dallas told leading referees at a course Thursday that players who mob the referee, and not only the initial offender, should be sanctioned, as well as those who run across the pitch to join an incident.

Excessive physical contact with the referee warranted more than a yellow card, he added.

Dallas also reiterated instructions about booking players who feign being fouled, warning that some players were refining their simulation skills during training.

"Why are they becoming very good at it? Because they are practising on the training ground how to cheat," he said. "We must drive this out of the game."