Haroon Barket Masih, president of the Masih Foundation, said Bibi had been kept in solitary confinement for more than three months.

He expressed concern over the conditions in which the mother-of-five is being held.

“She needs medical care, hygienic and healthy conditions,” he said.

“She fell ill with chickenpox because of the dirty environment, and being unable to clean her room or bed sheets on which she sleeps.”

Mr Masih said that in spite of her poor health, Bibi is spending her time fasting and praying for others.

“She neglects her health and prays for everyone else,” he said.

“She is concerned about the current situation in Pakistan.”

The Masih Foundation is providing financial and legal assistance to Bibi as she appeals her conviction.

The foundation is trying to arrange a medical examination for her. It says she has not received any medical care until now.

“Please continue to pray for Asia Bibi who prays and fasts,” he said.

Bibi was the first woman in Pakistan to be sentenced to death for blasphemy by a court last November.

There are grave concerns for her safety after the murders of Punjab Governor Salman Taseer, who had spoken in favour of a pardon for Bibi, and Minorities Minister Shahbaz Bhatti, who had been seeking changes to the blasphemy laws.

Bibi had to be relocated to a women-only prison after extremists threatened to blow up the previous prison in which she was staying.