Hong Kong activists on Friday said they rejected an official investigation which found a Chinese dissident had died of suicide, in a case which has sparked public protests.

Relatives and rights groups have said Li Wangyang, who was jailed for over 22 years for his role in the 1989 Tiananmen democracy protests, died in suspicious circumstances when he was found hanged at his hospital last month.

The Hunan provincial authorities -- where Li's hospital was located -- has launched a month-long probe and said in a report released late Thursday that the nearly blind and deaf activist had committed suicide.

"(The probe) confirmed that Li Wangyang died by using his bed sheet to hang himself," the report said, released by the Beijing-backed Hong Kong China News Agency.

The report also said DNA, CCTV recordings and fingerprints found on windows all confirmed only medical staff had entered his hospital ward.

Also included in the report was a written note allegedly from Li's sister and brother-in-law saying they had accepted the verdict and wanted to put the chapter behind them -- a claim disputed by Hong Kong activists.

"We don't accept the verdict," Richard Tsoi told AFP, the vice-chair of Hong Kong's main pro-democracy group, the Hong Kong Alliance in Support of Patriotic Democratic Movements of China.

"It is very vague and it raises more questions than answers. This is not an independent and impartial inquiry.

"We are also concerned whether Li's sister and brother-in-law have been forced to write the note under coercion because they still could not be contacted by their friends," Tsoi said.

Thousands of Hong Kongers have taken to the streets calling for answers about Li's death, while a senior official in the semi-autonomous Chinese city said the death was suspicious.

According to the New York-based group, Human Rights in China, two of Li's relatives found him strung up to a ward windowsill by a bandage wrapped around his neck, with his feet on the ground.

Li was under round-the-clock police surveillance in the hospital at the time, the group said.