Europe's top referees' official hinted on Monday that referees could strike after the retirement of Anders Frisk because of death threats to him and his family.

"We cannot just do nothing," sad Volker Roth, chairman of UEFA's [Images] referees' committee. "There will be a demonstration of solidarity among the referees as you have never seen before.

"I am really no friend of strikes but we must consider measures," he told Bild newspaper in his native Germany [Images].

Frisk is one of Europe's top referees and had been earmarked for the 2006 World Cup in Germany. He announced on Friday he was retiring, saying, "these last few weeks have been the worst of my life".

European soccer's governing body UEFA, who had hoped to persuade Frisk to return to the game, said in a statement on Monday that the Swedish referee's decision was final.

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"I have been in touch personally with Anders Frisk," UEFA chief executive Lars-Christer Olsson said in a statement. "His decision to retire is final and we must respect that.

"It is wholly unacceptable that a top international referee...is pressured into retiring this way."

The 42-year-old was in charge of Barcelona's 2-1 first leg victory over Chelsea in the Champions League last month. Chelsea coach Jose Mourinho said his Barcelona counterpart Frank Rijkaard had talked with Frisk in the dressing room at halftime in Spain.

Chelsea striker Didier Drogba [Images] was sent off by Frisk early in the second half. There were scuffles in the tunnel after the game and Chelsea refused to attend post-match news conferences. Chelsea won the second leg 4-2 to reach the quarter-finals.

"Of course, we make mistakes like every player and coach. But that shouldn't lead to referees being sworn at or even threatened," Roth said in a statement on the German Football Association's website.

"But if things escalate and millimetre decisions, which can only be decided after three slow motion replays, trigger exaggerated reactions, then the possibility exists that even the best referees in the world will abruptly give up."

World body FIFA's president Sepp Blatter said: "I am appalled by the verbal attacks directed at referees. It is often such extreme behaviour that sparks off trouble among supporters.

"I strongly urge everyone concerned to show respect towards referees and demonstrate fair play."

"Anyone who attacks a referee, attacks the football environment in which he lives.

DEMONSTRATE FRUSTRATION

Roth said in a statement a strike by referees in the Bundesliga would be the "very last means" with which to demonstrate their frustration at their treatment.

At the weekend Roth told a Swedish newspaper that "people like Mourinho are the enemy of football". He will hold a regular meeting with Germany's top referees on Tuesday in Frankfurt.

"It's obvious that our first reaction was of solidarity and compassion," William Gaillard, UEFA spokesman said on Monday.

"Players, coaches and managers have a responsibility to exert restraint. The game is watched by millions of people, we can't expect everyone to be as mentally balanced as they should be," Gaillard told Sky Sports news.

"One should be very careful about making statements that could be potentially inflammatory."

Frisk was also hit on the head by an object thrown from the crowd at AS Roma's Olympic stadium in September during a Champions League match against Dynamo Kiev.

"I think people should keep in mind that these are not highly paid people, they're not like the players or the coaches," said Gaillard.

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