A Chinese dissident who died in detention last month is one of three nominees for an award often dubbed the Nobel prize for human rights, organisers said Wednesday.

Cao Shunli, who died in mid-March at the age of 52, was hailed by the Martin Ennals Award organisers as an activist who since 2008 had "vigorously advocated for access to information, freedom of speech and freedom of assembly."

Bangladeshi activist Adilur Rahman Khan, who has worked to document extra-judicial killings, illegal detention, and enforced disappearances was also nominated for the prize, as was migrant and indigenous community rights activist Alejandra Ancheita of Mexico.

The winner of the award, which is attributed by a jury of 10 non-governmental organisations including Amnesty International and Human Rights Watch, will be announced in Geneva in October.

Cao is the first person nominated posthumously for the prestigious prize, Michael Khambatta, a spokesman for the organisers, told AFP. He said the nominees were agreed upon before news of her death emerged on March 14.

The dissident was detained last September shortly before she was due to travel to Geneva to attend a UN session on China's right's record.

She had been denied medical treatment for several months after falling ill, according to her family and lawyers, who maintain she was only sent to hospital after suffering organ failure and falling unconscious in late February.

China has insisted that her rights were protected all along and denied that she was mistreated.

The Martin Ennals organisers deplored that Cao had already spent more than two years in China's "re-education through labour system" and met with "repeated harassment", before her final detention.

"This is a tragic example of reprisals suffered by human rights defenders who work with international human rights mechanisms," they said, calling for an independent probe into her death.

The Martin Ennals Award is named after the former secretary general of Amnesty International. It was created in 1993, two years after his death.

Its inaugural recipient in 1994 was also from China -- rights activist and former political prisoner Harry Wu, who moved to the US in the mid-1980s and became a citizen in 1995. No Chinese national has won the award since.

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.