A Briton was detained by police at the Olympics today after unfurling a Free Tibet banner in protest at human rights abuses.
Philip Kirk, 24, from St Albans, Hertfordshire, and an Australian-Canadian climbed the distinctive China Central Television building in the capital Beijing to unfurl the banner.
Han Shan, Olympics campaign co-ordinator for campaign group Students for a Free Tibet, said the banner read Free Tibet in English and Chinese.
Three other protesters were also detained as they watched the climbers in action.
Mr Shan said: "The others detained were three Americans who were acting as support and to ensure the safety of the climbers and engage with the authorities."
He added that Nicole Rycroft, 41, was the other climber.
Last week two British Free Tibet campaigners - Iain Thom, 24, from Edinburgh, and Lucy Fairbrother, 23 - were deported after unfurling a 140-square-foot banner reading "One World, One Dream, Free Tibet" in Beijing.
Today's protest is the latest in a series of protests in the capital over alleged human rights abuses by the Chinese in Tibet.
Mr Shan said Mr Kirk was an avid climber who worked in a climbing shop and also a photographer who had been an active member of the organisation for a number of years.
He added that Mr Kirk had gone to Swansea Metropolitan University.
Mr Shan named the three Americans as Bianca Bockman, 27, from Hoboken, New Jersey, Sam Maron, 22, from New York and Kelly Osborne, 39.
Tenzin Dorjee, deputy director of Students for a Free Tibet UK, said his organisation is "working closely" with the arrested activists.
Mr Shan said: "As an experience rock climber and mountaineer, Phil learned about the injustices in Tibet through the climbing community.
"Last year Phil was horrified to learn that Tibetan refugees had been shot and killed by Chinese border authorities as they crossed Nangpala pass in an attempt to flee to Nepal.
"The shootings were captured on tape by climbers at Cho Oyu base camp on Mount Everest.
"It was at that time when Phil decided to get involved with the Tibetan Freedom movement and realised he could use his climbing skills in his effort to support the Tibetan People."
The pair abseiled down the building's glass facade and hung their banner over an Olympics billboard with the slogan "Beijing 2008" at 5.45am local time, a spokesman from Students for a Free Tibet said.
The group was arrested around half an hour after the climbers were first spotted by security officials, he said, adding he did not know where they were being held.
The building, which consists of two L-shaped high-rise towers linked at the top and the bottom, is the new headquarters of China's state television service and was completed just before the start of the Games.
Lhadon Tethong, executive director of Students for a Free Tibet, said: "While the Chinese government has built a gleaming new building for its official mouthpiece and its public relations strategy has become more sophisticated, the propaganda it uses to maintain its iron-fisted control over Tibet remains the same.
"Tibet supporters took action at CCTV today to broadcast a message of truth about the intensifying military crackdown in Tibet and the Tibetan people's undying resolve to regain their freedom."
A spokesman for the British embassy in Beijing said: "We are in touch with the Chinese authorities and we are seeking further details."
Officials expect Mr Kirk to be deported, probably later today.
Mr Kirk's mother, Wendy Charlton, told the Press Association she was proud of her son's efforts to draw attention to the Tibetan cause.
She said: "Obviously you're always worried when your child is arrested, especially abroad, but we are also very proud of what he is doing for the Tibetan people. I am very pleased he is highlighting their plight.
"China seems so normal when you watch the Olympics on television, but you can't say what you want to say there."
Ms Charlton, 54, who prefers to use her maiden name, said her son was an experienced climber and had prepared for the ascent of the CCTV building.
"I know he practised beforehand to make sure they would be as safe as possible. They wanted to do (the protest) peacefully, but it is always a worry."
She described her son as an "ordinary, outgoing person who loves climbing and is passionate about the Tibetan cause".
Today's stunt is not the first time his commitment to the Tibetan cause has got Mr Kirk into trouble with the authorities.
He was arrested in Paris in April after abseiling off a bridge over the River Seine and unfurling a banner protesting against the Olympic torch, which was passing through the city on its way to Beijing, according to Students for a Free Tibet.
Mr Kirk, who graduated from university last year and now lives with his parents and younger brother and sister, was released without charge shortly afterwards.