The life of a German-Iranian detained in Iran is in danger and she is in such pain she can barely move, a fellow prisoner who is a prominent rights activist said Sunday.

Nahid Taghavi, 68, was sentenced to 10 years and eight months in jail in August 2021 after being arrested at her Tehran apartment in October 2020, and is being held in solitary confinement at Tehran's Evin prison.

Even after recent releases, more than a dozen Western passport-holders remain detained in Iran, held according to rights groups as part of a deliberate policy of hostage-taking by Tehran to extract concessions.

"The life of Nahid Taghavi, a political prisoner, is in danger," her fellow inmate in Evin prison, the prize-winning campaigner and rights activist Narges Mohammadi, wrote on Instagram.

Mohammadi's Instagram account is run by her family in France based on her phone calls to relatives. Through this, despite her incarceration, Mohammadi continues to push for the rights of prisoners in Evin.

Taghavi was allowed brief medical leave in 2022, but according to her family she was returned to jail before she could recover.

"She can barely get out of her bed," wrote Mohammadi. "She goes to the infirmary, receives strong painkiller injections and returns to her bed."

"The pain is so severe it can be seen on her face," she added.

Mohammadi said that Taghavi had now spent 220 days in solitary confinement. This had worsened an existing spinal disc condition, and she was now also suffering from cervical disc problems, diabetes and high blood pressure.

Taghavi was convicted on national security charges along with British-Iranian Mehran Raoof, who is also still being held. Her family vehemently rejects the accusations.

Iran on Friday released one Dane and two Austrian-Iranian citizens in the wake of the release the week earlier of a Belgian aid worker.

Their liberation came after mediation by Oman and the release by Belgium of an Iranian diplomat convicted of "terror" offences, a move that troubled some rights groups.

Last month Iran also freed a French citizen and a French-Irish citizen, both of whom had been on hunger strike and the subject of increasing concerns about their health.