The referee at the centre of the feud between Chelsea manager Jose Mourinho and Barcelona coach Frank Rijkaard has quit the game after a series of threats.

Anders Frisk, a referee on the international stage for 16 years, claimed he could have put his family in jeopardy if he had carried on with the job.

The 42-year-old said: "The last few weeks have been the worst of my life. There have been threats on the phone and via e-mails and more usually in the post, and they've also affected my family.

"It's not worth continuing when it gets to this. My own and my family's safety come above everything.

"The threats have escalated in recent weeks after the match between Barcelona and Chelsea. Their tone has become much stronger. It's a real shame and an impossible task to try to beat something like this.

"In any case it's a battle I don't want to fight just because I'm a referee."

Mourinho claimed that Frisk and Rijkaard had a conversation at half-time in the referees' dressingroom at the Nou Camp in the first leg of the Champions League encounter. Chelsea won the tie over two legs.

Uefa are currently investigating a report about the incident from Chelsea.

Frisk is one of the world's most famous officials, having taken charge of 132 matches across the globe.

He also took charge of the Euro 2000 final between France and Italy.

However, this season has been a difficult one for the Swede, who found himself at the centre of attention earlier in the Champions League campaign when he was hit on the head by a missile thrown from the crowd during the game between Roma and Dynamo Kiev.

Frisk has likened his situation to that of fellow-referee Urs Meier, who found himself at the centre of attention after England were knocked out of Euro 2004 by Portugal.

The chairman of Uefa's referee's committee says coaches are indirectly to blame for the kind of incidents that prompted Frisk to retire and described Mourinho as "the enemy of football".

"It's the coaches who whip up the masses and actually make them threaten people to death," Volker Roth said. "We can't accept that one of our absolutely best referees is forced to quit because of this. People like Mourinho are the enemy of football."