An Iranian Christian convert has been released from Tehran's Evin prison after four years in detention.

Maryam Naghash Zargaran, 39, was arrested alongside Iranian-American pastor Saeed Abedini in January 2013 in connection with their work at an orphanage.

According to World Watch Monitor, she was released last night.

Zargaran was originally sentenced to four years imprisonment for acts that were 'in line with England and Occupied Palestine's [Israel's] anti-security agenda to spread Christianity in Iran in order to pervert Iranian society from Islam'.

She suffers from a number of medical conditions and had heart surgery 10 years ago. She has also been diagnosed with lumbar disc disease, arthritis and osteoporosis. Her congenital heart condition has reportedly been exacerbated by conditions in the prison.

Zargaran was denied treatment for her medical conditions in prison, being cited by Amnesty as an example of Iran's 'cruel' denial of medical care. She undertook several hunger strikes and was allowed to leave prison several times for medical treatment, but was forced to return each time before it was completed, World Watch Monitor says. Her sentence was extended by six weeks to reflect the time she spent outside prison.

Mansour Borji, from the advocacy group Article 18, told World Watch Monitor her 'unjust detention despite severe health issues is clear evidence of Iran's lack of respect for religious freedom'.

'Part of this suppression is reflected in the increased number of arrests, but also smear campaigns against religious minorities, especially Christians,' he added.