A Chinese human rights activist has died after falling critically ill in detention after police denied her medical treatment for months, her brother has said.

Cao Shunli, 52, who had engaged in peaceful activism for several years, died from organ failure on Friday at a hospital in Beijing, after five months in detention.

Her lawyer, Wang Yu, told the AFP news agency that Cao became ill in November but police denied her access to medical treatment for more than three months. Authorities sent her to hospital only when when she fell unconscious after suffering organ failure in late February, the lawyer said.

Cao's brother, Cao Yunli, said. "The police are responsible. Her body was weak, she was sent to the hospital too late."

Cao was set to travel to Switzerland to take part in a UN Human Rights Council review last September but police arrested her at Beijing's international airport.

She had joined a rare protest outside China's foreign ministry in June to demand greater participation in the UN's review of human rights in China, according to London-based Amnesty International and other rights groups.

"Cao Shunli's death exposes just how callous and calculating the Chinese authorities are prepared to be to silence critics. The authorities today have blood on their hands," said Anu Kultalahti, China researcher at Amnesty.

Cao suffered from tuberculosis in both her lungs, cirrhosis of the liver and uterine fibroids, the rights group said.

Beijing-based dissident Hu Jia said on his Twitter account: "The Communist Party should take full responsibility for her death."

Beijing police were not immediately available for comment on Cao's case.

China's ruling party maintains a close grip on power, and new leaders who took over in late 2012 have detained dozens of dissidents and tightened control over the Internet as well as social media.

China won a seat on the UN Human Rights Council in November along with Russia, Saudi Arabia and Cuba, despite fierce international criticism.

European countries and the US regularly condemn China on human rights, citing cases including its jailing of dissidents.

Beijing argues that its citizens enjoy increasing freedoms thanks to decades of rising prosperity.

Source: AFP