Six foreign activists have been detained for holding a protest on the Great Wall of China.
The activists called for an independent Tibet, and claimed the International Olympic Committee was not holding China accountable for human rights abuses.
The protest comes as China gets ready to mark a year before the Beijing Olympic Games begin, on 8 August 2008.
The games countdown has also brought protests from other groups, including Amnesty and Reporters without Borders.
The activists - from Canada, the US and Britain - unveiled a banner reading "One World, One Dream, Free Tibet 2008", on the side of the Great Wall.
"One World, One Dream" is the motto for the 2008 Beijing Olympics.
Activists say China is using the Olympics to try to legitimise its claims on Tibet, which it says it has ruled for centuries - a fact many Tibetans dispute.
The protesters were on the Wall for about two hours before being detained, according to the group they were with, Students for a Free Tibet.
They were not the only protesters using the Olympic countdown to highlight Chinese human rights violations.
Amnesty International has warned that the image of the games will be tarnished unless China acts urgently to stop abuses.
In a report, the group accused China's authorities of detaining activists and journalists without trial, in a "clean up" of the capital.
"Official statements suggest that the Olympics are being used to justify such repression in the name of 'harmony' or 'social stability' rather than acting as a catalyst for reform," said Amnesty's report.
The organisation said China had taken some positive steps in recent months by reforming the death penalty and relaxing restrictions on foreign journalists.
But Irene Khan, the organisation's secretary general, said they had also "tightened up the ability of Chinese journalists to work".
"We've also seen increasing arrests of human rights activists, an increasing use of 're-education' through forced labour, and what they call enforced drug rehabilitation," she said.
The Amnesty report follows a visit to Beijing by the Paris-based organisation Reporters Without Borders, which called for the release of more than 80 jailed journalists and dissidents in China.
China is gearing up to celebrate one year to go before the Olympics
Members of the organisation demonstrated near the Olympic headquarters, wearing black T-shirts showing handcuffs in place of the Olympic Rings.
"We didn't come to call for a boycott," said Vincent Brossel, a spokesman for the group. "We are calling for concrete achievements, the release of political prisoners, opening of Web access and an end to radio jamming."
Meanwhile organisers of the Beijing Olympics have repeatedly expressed a desire to keep the games non-political.
Speaking before the Amnesty report had been issued, Jiang Xiaoyu of the Beijing organising committee said: "We welcome even more constructive criticism on faults and problems."
But he said politicising the event did not "accord with the Olympic spirit".