BEIJING - An elderly doctor who embarrassed China's government by exposing blood-selling schemes that infected thousands with HIV has been stopped from going to Washington to be honoured by a charity supported by Hillary Clinton, a friend said Monday.

Retired physician Gao Yaojie, in her 80s, is among China's most prominent and tenacious AIDS activists. She has received numerous awards for efforts a decade ago to alert people in her home province of Henan, in eastern China, to an AIDS outbreak being spread by tainted blood transfusions.

Henan authorities warned Gao not to attend the Vital Voices Global Partnership awards ceremony next month but she refused to comply, said Hu Jia, a Beijing-based AIDS activist and friend of Gao's.

Zhengzhou city authorities put her under house arrest Thursday ahead of a planned trip to Beijing on Sunday to apply for a U.S. visa, Hu said.

He said friends and family who tried to visit Gao at home were being blocked or interrogated before being allowed in, and her daughter was under constant police surveillance.

Gao was refused a passport in 2001 to go to Washington to accept an award from a UN group.

A man who answered the phone at the Zhengzhou Public Security Bureau refused to answer questions about Gao. Like many Chinese officials, he refused to give his name and referred calls to the provincial government.

A Henan government official, who would identify himself only by the surname Wu, said he was unclear about the case.

Gao's and her daughter's phone numbers both rang unanswered Monday.

Hu said Gao was to be honoured for her work promoting women's legal rights in China at a March 14 Vital Voices annual awards dinner in Washington. Clinton is one of the group's honorary chairwomen.

Vital Voices could not be immediately reached for comment.

Gao's activism began in 1996 when she wrote and printed copies of a basic AIDS information pamphlet for distribution at Zhengzhou's long-distance bus stations.

Since then, she has distributed medicine, cared for AIDS orphans, written a book about China's AIDS epidemic and hosted AIDS sufferers in her modest apartment. Funding comes from her own earnings and occasional donations.