US Secretary of State Hillary Clinton has said she will press China on the issue of human rights when she visits Beijing this week.
However, Mrs Clinton would not comment publicly on the case of the prominent activist Chen Guangcheng.
Mr Chen escaped from house arrest last week and is believed to be under the protection of the United States embassy in Beijing.
US officials have kept an unusually solid wall of secrecy over the case, refusing even to say Mr Chen's name.
However, President Barack Obama and Mrs Clinton both said yesterday that they would press for human rights in China.
"A constructive relationship includes talking very frankly about those areas where we do not agree, including human rights. That is the spirit that is guiding me as I take off for Beijing," Mrs Clinton said.
Experts said they saw few easy ways to resolve the case of Mr Chen, who has said that he and his wife suffered severe beatings for defiantly speaking out after he completed a four-year jail sentence.
Mr Chen, 40, is said to want to stay in China, but US officials would be unwilling to hand him over without strict safety guarantees.
