Four protesters including two Britons have been detained in the Chinese

capital after hanging Free Tibet banners close to the main Bird's Nest stadium.

The demonstration underlined the clash between competing views of the Olympics in Beijing, as thousands of euphoric spectators cheered the arrival of the torch in Tiananmen Square while foreign activists launched a series of small protests around the city.

Given the massive security operation in the capital and the carefully organised audience, no one expected demonstrations in or around the square during the relay.

Crowds chanted: "Go Olympics - Go Beijing" as the basketball star Yao Ming, one of the nation's biggest sporting heroes, carried the flame past the portrait of Mao Zedong which hangs on the Tiananmen gate.

US and British campaigners scored a publicity coup by climbing electricity poles at dawn and unfurling outlawed Tibetan flags and banners with Free Tibet slogans in Chinese and English. Their protest took place just outside the Bird's Nest, where the opening ceremony will take place on Friday.

"We've done this action today to highlight the Chinese government's use of the Beijing Olympics as a propaganda tool to whitewash their human rights mobile phone conversation posted on the internet," said Iain Thom, one of the protesters, in a recorded mobile phone conversation posted on the internet.

The state news agency Xinhua said police ended the protest in 12 minutes, while Students for a Free Tibet said they were there for an hour before security officers led them away peacefully. The group said Thom, 24, was from Scotland while another protester, Lucy Marion, 23, was from England.

"As far as we know foreigners gathered illegally and we express

our strong opposition to that. We will resist all attempts to politicise the

Olympics," said Sun Weide, a spokesman for the Beijing organising committee. "We have laws regarding assembly and demonstrations, and we hope that foreigners will respect the laws of China."

Sun said the demonstrators had not been arrested or taken to a police station. No one had been able to contact the activists by this afternoon

because their phones were off. A British embassy spokesman said it was requesting immediate consular access.

In a separate incident, a European activist arranged the screening of a

film about Tibetan views of the Olympics in Beijing. It was halted when his hotel asked reporters to leave, but public security officials waiting at the venue did not intervene directly or approach the man when he left the building.

The video began with an introduction by Dechen Pemba, a Briton of Tibetan descent deported from the capital last month for "splittist activities". At the time, she said she had been in China solely in a private capacity and was not involved in any organisations.

The Tibet issue has dogged the Olympics since March's violent riots in

Lhasa and wider protests across Tibetan areas led to a security clampdown. Activists responded with demonstrations along the international leg of the torch relay, in turn sparking anger among the Chinese and making them all the keener to focus on celebrations as the flame returned to the capital.

Other protests today included a low-key demonstration by three

Americans who stood in Tiananmen Square - well after the torch had passed through - to shout a denunciation of China's population control policies. Police allowed them to leave the area after questioning them briefly.

Journalists received messages summoning them to two hotel rooms in Beijing containing dummies splattered with red paint. The walls had been defaced with slogans including: "One World, Our Nightmare" - a play on the Olympic "One World, One Dream" message - and a list of jailed dissidents. It was not clear who carried out the protest.

The US swimmer Amanda Beard, an Athens 2004 gold medallist, unveiled an anti-fur advert outside the Olympic village after the authorities prevented her from her staging a news conference in a hotel for "safety" reasons.

The government has designated zones for protest in parks around the city, but human rights campaigners warn that Chinese citizens will be deterred from taking part by the fear of reprisals and several groups have already been denied permits.

Other activists have been unable to enter the country. Team Darfur, a coalition of athletes seeking to draw attention to the conflict in Sudan, said that Beijing yesterday revoked the visa of its co-founder and Olympic gold medallist Joey Cheek.

He called the decision "part of a systemic effort by the Chinese government to coerce and threaten athletes who are speaking out on behalf of the innocent people of Darfur".

Activists argue China has the greatest leverage of any nation over Khartoum because of its oil purchases from and arms sales to the government. Emmanuelle Moreau, an International Olympic Committee spokeswoman, said organisers should expect people to use the platform of the Olympics to draw attention to their causes.

She said: "The IOC are confident Beijing city authorities will assess the

situation reasonably and act with tact and understanding."