BEIJING » The founder of a prominent AIDS activist group in Beijing has left China for the United States with his family because of increasing pressure from the government, he and his supporters said Monday.

The activist, Wan Yanhai, his wife and their 4-year-old daughter spent the weekend at the home of a friend in Philadelphia after flying from Hong Kong on Thursday.

In recent months, the group that Wan led, the Aizhixing Institute, had come under increasing scrutiny from tax officials and even the fire department, he said.

“;The Chinese government made it impossible for Wan Yanhai to remain in China,”; said Kate Krauss, the friend in Philadelphia and the director of the AIDS Policy Project, which advocates for more research into a cure for AIDS.

Wan said in a telephone interview, “;We were getting a lot of attention from different government agencies.”;

He added: “;When I work in China, they can really find a target to attack. When I left, they no longer had a target.”;

Wan is arguably the most outspoken AIDS campaigner in China. He founded Aizhixing in 1994 to support the cause of AIDS awareness and prevention. At the time, the Chinese government was reluctant to speak publicly about AIDS.

Wan helped turn an international spotlight on villages in Henan province where residents had become infected with HIV in the 1990s because of poor government oversight of blood transfusions. He was detained for four weeks in 2002 because of that advocacy.

Although Wan and his group had come under pressure before, the latest scrutiny coincides with a wider crackdown on civil society groups and grass-roots organizations that operate independently of the government. The authorities have been especially wary of groups that receive any financing from abroad and have imposed new restrictions on such financing.

On Monday, a man named Lei Yang answered the telephone at the Aizhixing office in Beijing and said the group was still working. When asked about Wan, he said, “;I am not aware of this situation.”;

Krauss said Wan had told her of how officials from several government departments in Beijing had made recent visits to the Aizhixing office. The tax officials who arrived were from a municipal authority, which was unusual, Krauss said. Fire department officials entered the office to see whether the office was complying with fire safety codes, she said.

“;I wonder if it's a way to expel him without publicity,”; said Krauss, who advocated for Wan's release when he was detained during the four-week period. The Chinese government has used administrative pressure to shut down civil society groups in the past year.

One notable case occurred in July 2009, when tax officials scrutinized foreign financing that was supporting Gongmeng, a legal research organization in Beijing. Gongmeng, or Open Constitution Initiative, had been taking on controversial legal cases and openly questioning central government policy, and it was forced to shut down after the investigation by the tax officials and after one of its leading members, Xu Zhiyong, was detained. Xu was later released.