The French President Nicolas Sarkozy today became the first major world leader to threaten China with an Olympic boycott in protest at the crackdown in Tibet.

He said he could not rule out refusing to attend the opening ceremony of the Beijing games.

Mr Sarkozy has come under increasing domestic pressure to take a stance over the unrest. He said he has not yet made a decision on what to do, but the mere suggestion of a boycott represented a clear threat to Chinese authorities.

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A French boycott of the August opening ceremony would have extra importance because France will hold the rotating EU presidency during the games.

Asked whether he supported a boycott, Mr Sarkozy said he could "not close the door to any possibility".

"Our Chinese friends must understand the worldwide concern that there is about the question of Tibet, and I will adapt my response to the evolutions in the situation that will come, I hope, as rapidly as possible," the president said.

Violent protests in Tibet, the most serious challenge in almost two decades to China's rule in the region, are forcing human rights campaigners and governments to re-examine their approach to the Olympic Games.

A French-based media freedom group, Reporters Without Borders, last week appealed for an opening ceremony boycott by heads of state and government, as well as royalty - an idea that has gained the support of many French.

In a poll for Liberation newspaper, 53% said they were "rather favourable to the idea of Mr Sarkozy staying away from the opening ceremonies.

Reporters Without Borders made headlines again yesterday when three high-ranking members were arrested at the Olympic flame-lighting ceremony after unfurling a black banner showing the Olympic rings as handcuffs.

Jean-Francois Julliard, the group's research director, welcomed Mr Sarkozy's comments.

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"We feel that things are starting to get moving, that political leaders are starting to change their attitudes," he said today. He was one of the three arrested in Greece and charged with "insulting national symbols."

He said that to his knowledge, Mr Sarkozy was the first world leader to go so far in the boycott discussion. Prince Charles has said he will skip the Olympics.

France has wobbled on how to handle the sensitive issue. Pierre Moscovici, a leader of the opposition Socialists, was quoted in a French newspaper over the weekend as criticising Mr Sarkozy for a "deafening silence" about the situation in Tibet.

France's foreign minister, Bernard Kouchner, suggested last week he was open to a boycott of the Beijing Olympics' opening ceremonies, calling it an "interesting idea." Later he backtracked, calling it "unrealistic" and saying, "We're not in favour of it."

France's Foreign Ministry said today that EU countries are to discuss the crackdown in Tibet at an informal meeting of foreign ministers on Friday in Slovenia.

Mr Sarkozy said he has told Chinese President Hu Jintao of his concern, asking for restraint and the end of violence through dialogue in Tibet. Mr Sarkozy also disclosed contacts between his office and that of the Dalai Lama, Tibet's exiled spiritual leader.

"I have an envoy who spoke to the authorities who are closest to the Dalai Lama," Mr Sarkozy said. "I want dialogue to begin, and I will gauge my response based on the response that the Chinese authorities give."

The Dalai Lama will be in France while the games are under way in Beijing. He is there principally to deliver Buddhist lectures.