Hopes that Nazanin Zaghari-Ratcliffe was about to be released temporarily from prison in Iran have been put in doubt, after the Iranian ambassador to the UK qualified a tweet suggesting she was about to be let out.

Zaghari-Ratcliffe, a British-Iranian dual national, has been in prison since 2016. On Saturday her husband Richard Ratcliffe said he believed she had contracted the coronavirus, which has spread through the country at an alarming rate.

In his initial tweet on Tuesday, Hamid Baeidinejad, the ambassador in London, wrote: “Mr [Gholamhossein] Esmaili, the spokesman of Iran’s judiciary, announced that Mrs Nazanin Zaghari is in good health condition and has not been affected with coronavirus. He added that one of the prisoners with security charge will be granted a furlough today or tomorrow to join family.”

But in a later tweet, Baeidinjad said a news agency report of Esmali’s statement that he had referred to had been “an interpretation”.

According to another Iranian news agency report, Hengameh Shahidi, a women’s rights activist who had been held in the same cell as Zaghari-Ratcliffe, was being released on furlough. Shahidi had been coughing and complaining she was ill in recent days.

It was unclear whether the muddle is simply human error or denotes a struggle between the ministry of foreign affairs and the judiciary.

There has been intense political pressure in the UK for Zaghari-Ratcliffe to be released ever since her husband said she was showing symptoms of the coronavirus. At no point has she been told about a possible temporary release.

Iran’s judiciary has already released hundreds of non-political prisoners temporarily, apparently because authorities have recognised that the risk of the coronavirus spreading through Iran’s crowded and insanitary prisons is so great that some action has to be taken.

Richard Ratcliffe said at the weekend that his wife was suffering symptoms of the disease, but Esmaili said at a press conference in Tehran that she was fine and she would be speaking to her husband later on Tuesday.

Zaghari-Ratcliffe has taken furlough once before, believing it would lead to her permanent release, but then rejected a further offer, saying she found the experience of returning to jail too traumatic. She has been charged with spying and is serving a five-year sentence that could be extended.

The UK, France and Germany have sent up to €5m (£4.4m) of health equipment via the UN to help Iran deal with the coronavirus outbreak, and that help, alongside political pressure from the UK, may have led Tehran to reconsider its previous position that no political or security prisoner should be released.

A previous judicial decree has allowed some political prisoners to go on furlough until 3 April, but this applied only to women over the age of 60 and men over 70. The sentence also had to be shorter than five years.

Zaghari-Ratcliffe’s constituency MP in north-west London, Tulip Siddiq, said on Tuesday: “If this furlough happens, the British government has an obligation to make it permanent and not let her be used as a bargaining chip in the weeks to come. I remain concerned that Nazanin has told her family that she has still not been tested for coronavirus.”

Ratcliffe said on Monday evening that the Iranian foreign ministry had falsely told the Foreign Office she had been tested for the disease and confirmed to be negative. He said his wife denied she had been tested.

Ratcliffe said his wife had been told nothing of her potential release as of Monday. “Nazanin would be very, very pleased to come out of prison,” he said. “However, I think it is a game by the Iranian authorities to avoid responsibility for testing and treating Nazanin for coronavirus.

“And our experience of furlough last time was very negative. It just made us a different kind of bargaining chip and the family were exposed to all sorts of threats from the Revolutionary Guards. So the UK government needs to make sure it can protect her and her family.”

• This article was amended on 3 February 2020 after Iran’s ambassador to the UK qualified a tweet implying that Zaghari-Ratcliffe was about to be released.