Nazanin Zaghari-Ratcliffe, the British-Iranian woman jailed in Iran for alleged spying, is now in a hospital psychiatric ward, her husband says.
Richard Ratcliffe said his wife was being held by the Iranian Revolutionary Guard in a Tehran hospital and the family feared she was being isolated.
It comes after Mrs Zaghari-Ratcliffe, 40, went on hunger strike for 15 days last month in protest at her detention.
She was jailed in 2016 after being convicted of spying, which she denies.
In a press release, the Free Nazanin Campaign said it was not known what treatment she was receiving or how long she was expected to remain in hospital.
Her father said he visited the hospital on Tuesday but was not allowed to see his daughter and that she has not been allowed to contact her family.
The campaign said before being transferred, Mrs Zaghari-Ratcliffe had told relatives: “I was healthy and happy when I came to Iran to see my parents.
“Three and a bit years later and I am admitted to a mental health clinic.
“Look at me now – I ended up in an asylum. It should be an embarrassment.
“Prison is getting harder and harder for me. I hate being played in the middle of a political game. I just hate it.”
Her transfer follows her hunger strike last month in protest at her “unfair imprisonment”, during which time Mr Ratcliffe also did not eat and camped on the pavement outside the Iranian Embassy in London.
In January, Mrs Zaghari-Ratcliffe went on a three-day hunger strike in protest against being denied specialist medical care.
Mr Ratcliffe said he had felt “euphoric” when he first heard his wife had been moved to a hospital. thinking it could be a prelude to getting treatment or even her release.
However, after her father was refused access to visit her in hospital or even allowed a phone call, the family has grown increasingly concerned.
“Are they isolating her again to squeeze her?” he said, in an interview on BBC Radio 4’s Today programme, suggesting the Iranian Revolutionary Guard may be putting pressure on her to sign various denouncements.
He said he had asked embassy officials to visit her as soon as possible.
Earlier he said it was “unnerving” not knowing what was happening, adding he would follow up the case with the next prime minister.
Earlier this year, foreign secretary and Tory leadership hopeful Jeremy Hunt granted Mrs Zaghari-Ratcliffe diplomatic protection in a bid to resolve her case.
In 2017 Boris Johnson, his rival to become Conservative leader and prime minister apologised after saying that Mrs Zaghari-Ratcliffe was in Iran “teaching people journalism” – despite her family’s insistence she was there to visit relatives.
He also told MPs the government was in “no doubt that Mrs Zaghari-Ratcliffe was in Iran on holiday and that was the sole purpose of her visit”.
He has repeatedly said the responsibility for her continued detention lies with the Revolutionary Guard.
In a statement, the Foreign Office said it was “extremely concerned about the welfare of Mrs Zaghari-Ratcliffe”.
A spokesman said: “We urge Iran to allow family members to visit and check on her care as a matter of urgency.
“We will continue to call for her release at the highest levels.”
Mrs Zaghari-Ratcliffe was arrested at Tehran’s Imam Khomeini Airport in April 2016 and has always maintained the visit was to introduce her daughter, Gabriella, to her relatives.
The couple’s five-year-old daughter, Gabriella, has stayed in Iran with her grandparents since her mother’s arrest.
Before being transferred, she was being detained in Tehran’s Evin Prison.