BEIJING — A Chinese doctor who exposed the cover-up of China's SARS outbreak in 2003 has been barred from traveling to the United States to collect a human rights award, a friend of the doctor and a human rights group said this week.

The doctor, Jiang Yanyong, a retired surgeon in the People's Liberation Army, was awarded the Heinz R. Pagels Human Rights of Scientists Award by the New York Academy of Sciences. His army-affiliated work unit, Beijing's Hospital 301, denied him permission to travel to the award ceremony in September, Hu Jia, a Chinese rights promoter who is a friend of Jiang's, said Thursday.

The Information Center for Human Rights and Democracy, which is based in Hong Kong, also issued a statement reporting the rejection of the travel request. The doctor could not be reached at his home for comment, and a person who answered the phone in the director's office of Hospital 301 said the situation was unclear, declining to provide further details.

Jiang rose to international prominence in 2003, when he disclosed in a letter circulated to international news organizations that at least 100 people were being treated in Beijing hospitals for severe acute respiratory syndrome, or SARS. At the time, the Chinese medical authorities were asserting that the entire nation had only a handful of cases of the disease.

The revelation prompted China's top leaders to acknowledge that they had provided false information about the epidemic. The health minister and the mayor of Beijing were removed from their posts.

SARS eventually killed more than 800 people worldwide, and the government came under international scrutiny for failing to provide timely information that medical experts said might have saved lives.

Jiang was initially hailed as a hero in Chinese and foreign news media. He used his new prestige in 2004 to press China's ruling Politburo Standing Committee to admit that the leadership had made a mistake in ordering the military to shoot unarmed civilians on June 3 and 4, 1989, when troops were deployed to suppress democracy protests that began in Tiananmen Square in Beijing.

Jiang, who treated Beijing residents wounded in the 1989 assault, contended that the official line that the crackdown was necessary to put down a rebellion was false. His statement antagonized party leaders, who consider the crackdown a matter of enormous political sensitivity.

Jiang Zemin, then the leader of the military, ordered the detention of Jiang, who spent several months in custody, people involved in his defense say. Jiang was eventually allowed to return to his home but remained under constant watch. He has not been allowed to accept press requests for interviews or to visit family members who live in the United States, friends and human rights groups say.

Hu said that Jiang's superiors at Hospital 301 had told him that he could not travel to New York to collect his award because the ruling Communist Party was seeking to maintain an atmosphere of social and political stability in the period leading up to the 17th Party Congress in the fall, when party leaders decide on a new leadership lineup.

"There is always some big political event they can use as an excuse to put pressure on human rights defenders," Hu said. "The real reason is that they want to keep him under house arrest so he has no opportunity to speak the truth to the outside world."