In a statement, 10 independent United Nations rights experts highlighted the situation of lawyer and environmental rights defender Dang Dinh Bach, who they said had just launched his third hunger strike in detention.

"We are extremely concerned about the safety and well-being of... Mr Bach. On top of discrimination and differentiated treatment in detention, there are reports that Mr Bach was being attacked and beaten up in custody," the experts said.

Bach, who worked to inform people whose health and livelihoods were threatened by coal projects and other polluting industries, was arrested in June 2021, and was sentenced to five years in prison for tax evasion.

"We express our strong concern about the chilling effect that the mistreatment and deprivation of liberty of Mr Bach have on the fundamental freedoms of peaceful assembly and of expression in Vietnam," said the experts.

The experts, who are appointed by the UN Human Rights Council but do not speak on behalf of the United Nations, pointed out that Bach was being held eight hours away from his family, on whom he depended for food, as per his vegetarian diet.

Held in a wing of the Prison No. 6 in Nghe An province reserved for political prisoners, he has been deprived of supplies like books and hygiene items, and denied access to hot water and traditional medicines, they said.

Communication and visits from his family and his lawyer were also restricted, said the experts, who included the UN special rapporteurs on the situation of rights defenders and on freedom of expression, as well as members of the UN working group on arbitrary detention.

They pointed out that the working group concluded last year that Bach's detention was unlawful.

And they highlighted that he was held incommunicado during his pre-trial detention and following his sentencing, prosecuted in a closed trial and not permitted adequate access to his lawyer.

"Mr Bach should not have to embark on a hunger strike to demand strict enforcement of laws and dignified prison conditions," the experts said, urging Vietnamese authorities to "stop mistreating" him.

"Deprivation of liberty and mistreatment in prison should not be used as a tool by the Vietnamese government to silence human right defenders and civil society members working on sensitive issues," they said.