Police in the Chinese financial hub of Shanghai broke up a news conference by a group of haemophiliacs who say they contracted HIV/AIDS through contaminated blood transfusions, an activist said on Thursday.

Journalists were detained and police surrounded the hotel where the event was taking place, said Wan Yanhai, the widely respected director of the Beijing Aizhixing Institute of Health Education.

Calls to the Shanghai city government and police were not answered.

The group has been demanding compensation but the government has stymied legal efforts to sue the company they say provided the infected blood products, Wan said.

“We strongly and angrily condemn the Shanghai police for this action which seriously encroaches on the rights of citizens to free expression,” Wan said in a statement.

Last year, the central government said it would severely punish those responsible for serious diseases transmitted by transfusions. The move followed several cases in which people were infected after receiving blood sold by HIV carriers.

But health workers and AIDS activists say blood for transfusions is still not routinely tested for the disease.

Political sensitivity and social stigma still surround AIDS in China, and the government’s slowness to acknowledge the epidemic contributed to its spread, especially in the central province of Henan, where in the 1990s millions sold blood to unsanitary clinics.

There were about 25,000 deaths from AIDS across China in 2005. In January, Beijing lowered by around 30 percent the estimated number of people living with HIV/AIDS to 650,000, yet warned against complacency, saying the figure was still rising with many people unaware of the danger.