Image caption Li Wangyang (left) was jailed after China's 1989 democracy protests in Tiananmen Square

A leading Chinese dissident imprisoned after the 1989 Tiananmen pro-democracy protests has been found dead under strange circumstances, his relatives and rights groups said.

Officials said Li Wangyang, who was freed from jail a year ago, hanged himself in hospital, where he was being treated for heart disease and diabetes.

But Mr Li's brother-in-law questioned the death, saying Mr Li had showed "no signs of suicide" in a recent meeting.

Mr Li spent more than 22 years in jail.

'Strong spirit'

Zhao Baozhu said he saw the body of his brother-in-law in a hospital in the central Chinese city of Shaoyang.

Mr Li was found in his room with a white strip of cloth around his neck connected to a window bar above, Mr Zhao said.

He said the authorities had then taken away Mr Li's body without approval from the family.

"Last evening we were together, Li Wangyang did not show any signs of suicide; it is strange," Mr Zhao told AFP news agency.

"Li Wangyang is a man with a strong mind and strong spirit," he added.

He told the news agency he did not want to comment further as he was afraid his phone was being monitored.

The Hong Kong-based Information Centre for Human Rights and Democracy in China said Mr Li died "unusually".

"We cannot rule out that security guards monitoring him tortured him to death and faked a suicide," the centre said in a statement.

Mr Li, a labour rights activist, was sentenced to 13 years in prison for his role in the 1989 Tiananmen protests, the centre said.

He was released in 2001 but later sentenced to another 10 years for "inciting subversion".