Four foreign protesters displaying a "Free Tibet" banner in the Chinese capital Beijing have been held by police.
The two Britons and two Americans unfurled Tibetan flags and banners declaring "One World, One Dream: Free Tibet" and "Tibet will be free".
The three men and one woman gathered near the main Bird's Nest Stadium, where the Games will open on Friday, and two of the men climbed electricity poles to unfurl the banners.
A report from state media said police rushed to the scene after 12 minutes and took the group away.
"We did this action today to highlight the Chinese government's use of the Beijing Olympics as a propaganda tool," Briton Iain Thom said in a message recorded while he was unfurling a banner and released on the group's website. "They're whitewashing their human rights record on Tibet."
The protest was carried out despite unprecedented security around Beijing in the run-up to the Games.
"This is only the beginning of a sustained effort of non-violent action that will bring attention to human rights abuses in Tibet, and that will happen throughout the Olympics in Beijing and around the world," said a spokesperson for the group Students for a Free Tibet.
China's Olympic organisers condemned the protest.
In April, the group staged a protest at Mount Everest base camp against plans to take the Olympic torch to the mountain and unfurled a giant banner along the Great Wall of China exactly a year before the opening ceremony.