Barcelona president Joan Laporta has launched a crackdown against a group of notorious hooligans ahead of the club's Champions League clash with Chelsea.

The Boixos Nois (Mad Boys) have been blamed for a series of incidents with the latest being an attack by a fan on a club security guard at the team hotel in Germany ahead of Tuesday's quarterfinal with Bayern Munich.

Barcelona will be visiting Chelsea on 6 May for the second leg of their semi-final and Laporta is now stepping up his efforts to stop the troublemakers. The chief, who has received death threats from the group, said the club knew the identity of its members and were drawing up plans to prevent them travelling to away matches and gaining access to grounds.

"We have to talk less and act more," he said. "Either we take steps to prevent them from travelling and getting into the stadiums or we'll see more serious incidents. We will continue to act with the same forcefulness and we will make no concessions to the aggressors."