Chinese dissident Chen Guangcheng is reportedly in the US embassy in Beijing after earlier escaping house arrest in the east of the country.
Mr Chen is a blind self-taught lawyer who was imprisoned after uncovering a series of rights abuses in China.
He is thought to have left his home in Shan-dong province on Sunday and released a video appealing directly to the central government.
The 40-year-old had been under house arrest since being released from a four-year jail sentence in 2010.
The overseas rights group, China Aid, has said Mr Chen is under US "protection", with Washington and Beijing in talks over his status.
The Shan-dong government has said it has no comment on Chen's escape and state media has made no mention of the story.
The US has expressed concern about Mr Chen, but refused to comment on his whereabouts or confirm reports that he was in a US embassy.
China Aid is run by Bob Fu, a former Tiananmen Square democracy activist who fled China for the United States in 1996 but has been in close contact with Mr Chen and the supporters who helped him escape.
In a statement, the group said it had learned from a "source close to the Chen Guangcheng situation" that the activist was under US protection.
"High-level talks are currently under way between US and Chinese officials regarding Chen's status," said the statement, which also called on the United States to ensure the safety of the activist and his family.
If he has been given refuge at the embassy, it could prove a major diplomatic irritant just as China and the US are preparing for wide-ranging annual talks next week on their often difficult relationship.
