Chen Guangcheng, a blind Chinese legal activist who has escaped from home imprisonment, is believed to have gone into hiding in Beijing, amid unconfirmed reports he has taken refuge in the US embassy.
The Texas-based ChinaAid said it "learned from a source close to the Chen Guangcheng situation that Chen is under US protection and high-level talks are currently under way between US and Chinese officials regarding Chen's status".
"Because of Chen's wide popularity, the Obama administration must stand firmly with him or risk losing credibility as a defender of freedom and the rule of law," Bob Fu, president of the religious and political rights advocacy group that has long campaigned for Chen's freedom, said in a statement.
A self-schooled legal advocate, Chen had campaigned against forced abortions and forced sterilisations. Chen and his family had been restricted to his home and subjected to relentless surveillance since September 2010 when he was released from jail.
His treatment has fanned protests by Chinese sympathisers and criticism from foreign governments and activist groups.
'Strain' on US-China relations
The US has not given any public confirmation of reports that Chen, who slipped away from under the noses of guards and bristling surveillance equipment around his village home in Linyi in the eastern Shandong province, fled into the US embassy.
China has also declined direct public comment on Chen's reported escape, which threatens to overshadow a two-day meeting with top US officials, including Secretary of State Hillary Clinton, in Beijing from Thursday.
Chen's escape, reported on Friday, and the outcry it has caused could add to the headaches of China's ruling Communist Party, which is seeking to ensure stability and authority before a leadership transition later this year.
Hu Jia, a human rights advocate in Beijing who has supported Chen, told the Reuters news agency he believed Chen was under US diplomatic protection.
"It's clearly understood that his supporters took Chen Guangcheng to the safest place, and our understanding is that the safest place means the United States embassy," said Hu, who was himself jailed for his outspoken criticism of the Chinese government.
"If you ask other embassies whether they have Chen Guangcheng, they will say no. But if you ask the US embassy, they say nothing, so we believe he is there."
Later on Saturday, Hu was escorted away by a group of police, according to his wife Zeng Jinyan.
More police were likely to come to take her away as well, she said.
"The situation is very complicated. The police are outside right now," Zeng said in a strained voice before ending the conversation.
Pu Zhiqiang, a Beijing lawyer and rights advocate, said reliable contacts also told him Chen took refuge in US embassy grounds.
The incident will be another damaging blot on China's security services, Pu said.
""Everyone knew about the suffering of Chen Guangcheng and his family but nobody dared raised his head over this and ignored it."
- Pu Zhiqiang, Beijing lawyer
"Everyone knew about the suffering of Chen Guangcheng and his family but nobody dared raised his head over this and ignored it," he said, referring to Chinese officials. "Chen Guangcheng has been the most typical victim of this lawless, boundless exercise of power," said Pu. "But the day has finally come when he has escaped from it."
In a video posted on YouTube, Chen confirmed he had escaped, and asked Wen Jiabao, the Chinese premier, to order an investigation in the maltreatment of him and his family by local officials.
"It was not at all easy, but I have escaped," he said in the video. "Everything that was said on the internet about the violence directed against me by Linyi, I'm here to say that it was all true."
Chen did not say where he was or what his plans were. "I want Premier Wen to open a probe into this corrupt behaviour.
"The money paid by the people in taxes should not be wasted by corrupt local officials to hurt us," he said.
Stephen Vines, a Hong Kong-based political commentator, told Al Jazeera that Chen was "asking the authorities to stop the beatings of himself and his family.
"But on many occasions he's said he doesn't want to leave China, and I think it's unlikely he'll leave China without his wife and child, who he's not with now."