Ban Ki-moon, the secretary general of the United Nations, has indicated he will skip the opening ceremonies of the Beijing Olympics this summer, capping an extraordinary week of public relations disasters for the Chinese government as it struggles to contain international anger over its policies towards Tibet and Sudan.

Officials fudged the reasons for Mr Ban's decision citing scheduling conflicts. But he is only the latest world leader in recent days suddenly to have found reasons to duck the opening events, after a similar move by Gordon Brown. Mr Ban's absence will be especially symbolic as the UN and the Olympics are meant to share global ideals.

Making matters still worse for the hosts – and also for an increasingly jittery International Olympics Committee (IOC) which has been meeting this week in Beijing – has been the near pandemonium that has attended nearly every stage so far of China's much-heralded torch relay around the world.

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Yesterday, protests in Buenos Aires included the unfurling of a giant "Free Tibet" banner on the torch route and a rival march organised by members of the Falun Gong spiritual movement, which is banned in China. Although the protesters were in smaller numbers than were seen during the relays earlier in the week in London, Paris and San Francisco, more than 6,000 Argentinians had signed up to a petition calling on China to talk to the Dalai Lama before the torch had even arrived on Thursday.

China is becoming increasingly aggrieved at the demonstrations and the gathering pressure for it to distance itself from the government of Sudan because of the continuing violence in Darfur – and the crackdown in Tibet. Yesterday, the Foreign Ministry in Beijing lashed out at the United States Congress for passing a resolution on Wednesday urging China to open dialogue with the Dalai Lama. The government was "strongly indignant" at the US move, said a Foreign Ministry spokeswoman, Jiang Yu. "It is confusing black with white and is vicious-minded of certain members of the US House of Representatives to not only fail to condemn the attacks, smashing, looting and arson in Lhasa ... but rather to point the spear at the Chinese government and people."

The troubled torch relay continued to attract attention, meanwhile, with Wangari Maathai, a Kenyan Nobel Laureate winner, announcing she had pulled out of joining the Tanzanian leg of the relay because of China's human rights record.

Earlier this week, Downing Street officials confirmed Mr Brown would be among world leaders not attending the opening ceremonies in Beijing, although they also stopped short of calling his decision a boycott. The French President Nicolas Sarkozy is also said to be considering staying away, while Angela Merkel, the German Chancellor, had earlier made it clear she would not attend the opening. In the US, all three candidates for the White House, including John McCain, the Republic nominee, have urged President George Bush to decline the invitation.

Meanwhile, Tokyo has joined the fray with a warning that the strapping Chinese men in blue and white tracksuits who have been running alongside the torch as self-appointed bodyguards will not be welcome on Japanese soil.

When the flame arrives in the city of Nagano, site of the Winter Games in 1998, it will be Japanese police who will protect it and no one else, officials said.

A spokeswoman for the IOC expressed the hope that there would be no repeat of the scenes of chaos, in Paris especially, as the flame continues it progress around the globe. "We do hope the torch relay can progress with many more smiles and cheers and the kind of atmosphere it deserves," Giselle Davies said.

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But campaigners say protests are likely to continue following the torch as it makes its way across the globe. "It's definitely going to keep going," said Lhadon Tethong, executive director of Students for Free Tibet.

China's unflinching support for the Sudanese government is likely to become the focus of protests when the torch heads to Africa this weekend for a relay through the Tanzanian capital Dar es Salaam

The torch's arrival in India – home to Tibet's government-in-exile and the largest community of Tibetans outside of China – is expected to be met with particularly passionate protests.

A week of world protests

* SUNDAY: 37 people arrested in London as Chinese paramilitaries guarding the Olympic torch collide with the first concerted protests since the relay left Beijing on 1 April.

* MONDAY: British Government criticised for allowing Chinese secret service to help with torch security as thousands turn out to protest in Paris. The torch's Chinese minders forced to extinguish flame three times and carry it through Paris on the bus.

* TUESDAY: Torch heads to San Francisco where protesters vow to continue their campaign. The International Olympics Committee president, Jacques Rogge, says future relays may be restricted to the host country because of widening protests against the Chinese.

* WEDNESDAY: Protests force San Francisco relay's route to be halved and the closing ceremony to be cancelled. Police divert route away from protesters and whisk it to the airport in a heavily guarded motorcade. Few people – protesters and supporters – saw the flame.

THURSDAY: Gordon Brown is accused of dithering as he confirms he will not attend the Games' opening ceremony but will be there for the closing ceremony. He is backed by Hillary Clinton. Mr Rogge admits the global protests have thrown the Games into a "crisis" as torch arrives in Argentina. EU Parliament raises prospects for a leader boycott of the opening ceremony and US House of Representatives calls on China to enter into talks with the Dalai Lama.

* FRIDAY: Protests break out in Buenos Aires, and the UN secretary general, Ban Ki-moon, says he may not attend the opening ceremony citing "scheduling" problems. The Kenyan Nobel Peace Prize winner Wangari Maathai pulls out of the Tanzanian relay in protest at China and Japan says it will not accept help from Chinese security forces when the torch arrives in Nagano later this month.