The Vietnamese authorities have been accused of denying medical treatment to an imprisoned land rights activist, Tran Thi Thuy, in circumstances that could amount to torture.
Amnesty International said there were increasing fears for the health of Mrs Thuy, who has been diagnosed with a tumour on her uterus, and is in severe pain.
It accused the government of refusing treatment until she “confesses” to the charges against her.
Amnesty called for urgent action from its supporters, asking them to demand the immediate release of a prisoner of conscience imprisoned for peaceful activities in the defence of human rights.
Tran Thi Thuy was arrested with six other land rights activists in 2010 and later convicted, in a one day trial, of subversion against the state. She was sentenced to eight years in prison.
Her family members say she first became ill in April last year and the tumour was then diagnosed by the prison doctor.
They said she had not been provided with any treatment, and was told by an official that she would die in prison if she did not admit to her alleged crimes.
Her family have been able to provide her with traditional medicines.
Tran Thi Thuy is a Hoa Hao Buddhist who became involved in the struggle for land rights after her family had their land seized by local authorities.
Campaigners say dispossessed farmers are often offered low levels of compensation while their land is sold on to developers for large profits.
Amnesty International said that prison conditions in Vietnam are often harsh, with inadequate food and health care.
It said that Mrs Thuy was being held at a facility in the south of the country hundreds of kilometres from her home, making it hard for her relatives to deliver essential supplies of food and medicine.