The speaker of the US House of Representatives yesterday called on the international community to condemn China for its crushing of protests in Tibet, saying the crisis was a challenge to the "conscience of the world".

Nancy Pelosi, who leads the Democratic party in Congress, was the first foreign politician to meet the Dalai Lama since the bloody unrest spread across the roof of the world. Her appearance alongside the Tibetan spiritual leader at his home in the north Indian town of Dharamshala was condemned by Beijing, which accused her of meddling in China's internal affairs.

Pelosi's visit and strong language are the most serious breach in a western consensus that China's economic and strategic strength renders impossible any protest beyond verbal expressions of unease.

She did not call for an Olympic boycott, which the Dalai Lama has also opposed, but appeared to open the door to one if China maintained its crackdown in Tibet. She said the "world is watching" events there, and called for an international investigation into the violence, and access to the region for journalists and international human rights monitors.

Pelosi said it was incumbent on "freedom-loving people throughout the world" to speak out against China's "oppression". If they did not, "we have lost all moral authority to speak on behalf of human rights anywhere in the world".

There is no appetite among governments for an Olympic boycott. All have too much to lose by alienating the burgeoning superpower. But the news and images filtering through the razor wire around Tibet are making many western capitals uneasy, particularly those that promised to build foreign policies on human rights.

Ceremony boycott

The situation would have to worsen dramatically for there to be serious contemplation of a boycott. Activist groups are focusing instead on a demand for world leaders to stay away from the games' opening ceremony in Beijing, and on that front they could claim to have opened some cracks in the Olympic wall.

The White House insists that George Bush will not reconsider his plans to attend. But Bush's insistence that his presence at the games would be purely out of sporting enthusiasm and entirely apolitical is coming under increasing fire in the US, particularly in view of the 1980 US boycott of the Moscow Olympics, led by Bush's political idol, Ronald Reagan. Yesterday, John McCain drew attention to Bush's caution on the subject, saying that Tibet was "one of the first things I would talk about if I were president of the United States today".

"The people there are being subjected to mistreatment that is not acceptable with the conduct of a world power, which China is," McCain said.

Even before Tibet exploded there was some momentum in the US behind an Olympic boycott, driven by groups seeking to punish Beijing for its links to the Sudanese government, alleged to be behind counter-insurgency atrocities in Darfur. The film director Steven Spielberg had already declared he would resign as artistic director to the opening ceremony for that reason. Pelosi's stand is likely to add to that momentum and put it at the centre of the presidential election contest in which Democratic and Republican candidates are likely to find themselves under pressure from their own supporters.

In Europe Bernard Kouchner, France's foreign minister and a former human rights campaigner, became the first prominent official to break ranks when he described a proposal by the group Reporters Without Borders for an opening ceremony boycott as "an interesting proposal" that could be debated by EU foreign ministers when they meet next week in Slovenia.

The British were horrified, and an official in London suggested that Kouchner was "talking from the hip". Gordon Brown and the foreign secretary, David Miliband, have invested time and air mileage in cultivating China, and the prospect of a retaliatory boycott against the London Olympic games in 2012 is on British minds.

Whether it was after an irritated call from the Elysée Palace or not, the French foreign minister said in later interviews, that a boycott of the opening ceremony, "though not a bad idea", was unrealistic and the government was not in favour. He admitted that France's economic interests in China "complicated things" and cautioned against making threats that clearly would not be executed.

Bernard-Henri Lévy, veteran of the French left, in the Spanish centre-right paper El Mundo, called for a boycott of the games to "save sport, honour and many lives". Of Chinese attacks on Tibetan dissidents, he wrote: "In front of this cynicism I think that there is still time to make use of tough language." He added: "Will Beijing never cede? Will a boycott never work? We will never know unless we try."

Protest rally

In Italy the outgoing centre-left government and the rightwing alliance led by Sylvio Berlusconi, expected to win in next month's vote, both oppose a boycott, but the pressures beneath them are building. Several dozen members of parliament joined a crowd of up to 300 in a central Rome square on Wednesday under a banner proclaiming: "We are all Tibetans." At least three ministers in the outgoing government attended the rally, at which several speakers supported a boycott.

In Germany, there are signs of a public groundswell for some sort of protest. German TV is running a poll on the issue, and so far a majority supports staying away.

Bild newspaper yesterday quoted the foreign minister, Frank-Walter Steinmeier, warning China that its response to the crisis may jeopardise the Olympics.

"You can't just host glamorous events for television while things are going topsy-turvy in your own backyard," he said in an interview for today's edition. "The host has to allow thousands of journalists into the country. You won't be able to sweep anything under the carpet.

"The German federal government is saying to the Chinese government: be transparent. We want to know exactly what is going on in Tibet."

The federal government of the chancellor, Angela Merkel, is committed to holding a common line with the rest of Europe but Merkel has said Germany should find means to keep up pressure on Beijing. That pressure will be stepped up in May when the Dalai Lama makes his second visit to Berlin in less than a year.

The most concerted push for a boycott has come from the east, where memories of communist rule are still fresh. In Poland members of parliament this week sent a protest note to Beijing calling for the release of all political prisoners from Lhasa, warning China that it was breaking the Olympic charter and saying it was not too late for a boycott.