A Christian convert from Islam in Iran has been sent back to prison in spite of suffering long-term health issues.

Maryam Naghash Zargaran, who has gone on hunger strike twice while in prison, had been released last month to get medical treatement after serving three years of a four-year sentence.

On Saturday she was locked up again in the notorious Evin prison and had to cut short her treatment, according to World Watch Monitor.

Amnesty International has criticised Iran's lack of adequate medical care in its prisons as "cruel".

Zargaran is a convert to Christianity from Islam who was arrested in January 2013 in connection with her work at an orphanage alongside the Christian pastor Saeed Abedini, who has dual Iranian and US citizenship. He was also imprisoned but released in January this year and is now in the US.

There has been a spate of arrests in Iran in recent weeks. A further five Iranian Christians were arrested at the end of August and there is growng concern for their safety, persecution charity Open Doors reported.

Zargaran's health deteriorated considerably during the hunger strike, her blood pressure dropped, she had pains and numbness in her feet and suffered psychological issues as a consequence of her imprisonment. She ended the latest hunger strike at the request of her family at the beginning of August, said Open Doors, which is asking for prayers.