Boris Johnson will call his Iranian counterpart today after it emerged his comments about her case meant a British mother could be condemned to another five years in jail in Tehran.
Nazanin Zaghari-Ratcliffe was arrested in Iran last year after travelling to the country to take her young daughter Gabriella to visit her parents last year.
But she was arrested over allegations she was a spy plotting to overthrow the government - which she and her family denies - and was jailed for five years.
Last week Boris Johnson said Mrs Zaghari-Ratcliffe was 'teaching' journalism when she was arrested in 2016 and she was dragged back to court on a 'propaganda against the regime' charge which could add five years to her jail term.
Her husband Richard Ratcliffe told MailOnline Mr Johnson's incorrect comment has given the Iranians a chance to 'smear' his wife and hit her with fresh charges.
The Foreign Office said last night that Mr Johnson's comment was 'misrepresented' in Iran but did not off an apology or full retraction.
Mr Johnson will today phone his Iranian counterpart to underline his position and press for Mrs Zaghari-Ratcliffe's release, an official said.
Nazanin Zaghari-Ratcliffe with her husband Richard Ratcliffe and their daughter Gabriella. Mrs Zaghari-Ratcliffe was jailed for five years in Iran for spying but insists she is innocent and only in the country to visit her parents with her young daughter (file pic)
Nazanin Zaghari-Ratcliffe, pictured with her daughter Gabriella, could have her sentence doubled from five to ten years after the Foreign Secretary wrongly said she had been in Iran training journalists (file photo)
Boris Johnson, pictured entering Downing Street yesterday, will call Iran today to prevent a Briton having her jail term extended after he commented on her case
Downing Street said Mr Johnson and Theresa May have been working on the case for a 'long period'.
Mrs May's spokesman said work was underway to establish the 'facts' of the case and did not immediately express full confidence in Mr Johnson when pressed by reporters.
Shadow foreign secretary Emily Thornberry has called for Mr Johnson to resign if Mrs Zaghari-Ratcliffe faces an extended jail sentence because of his remarks.
The Iranian judiciary's High Council for Human Rights said the Foreign Secretary's statement had shed 'new light' on the case.
Mr Ratcliffe told Mail Online: 'That's why it is so important that he issues a retraction saying very clearly that she is innocent as far as he is concerned, and doing nothing other than visiting the country with her daughter.
'I'm still amazed that on day 583 the British Government still has not said 'this is a mum who's being held – this is crazy'.
'Rather than implying that she was doing something and therefore the criminal suspicions are justified.
'Not issuing a correction makes it look like he's endorsing what the Iranians are trying to do.'
April 2016: Arrested by the Revolutionary Guard in Tehran Airport after visiting her parents in Iran with her young daughter Gabriella.
She was taken to prison and held in solitary confinement for 45 days before being moved to a women's wing.
The mother-of-one was not given access to legal counsel or medical treatment, and the lights in her cell remained permanently switched on.
As a result,Mrs Zaghari-Ratcliffe experienced problems walking, weight loss, and hair loss.
September 2016: She was sentenced to five years in prison for spying following a trial campaigners have branded 'secret and unfair'.
April 2017: Mrs Zaghari-Ratcliffe lost her appeal to overturn her sentence.
November 2017: She is hit with fresh charges of spreading propaganda just days after Boris Johnson told Britain's Foreign Affairs Select Committee that she has been training journalists in Iran.
He said the fresh charge had come as a horrible bolt out of the blue for his wife in Iran.
He said: 'Nazanin was very shocked and just cried on the phone for most of the call on Saturday when she was taken to court.'
Mrs Zaghari-Ratcliffe is a dual British and Iranian national, but Tehran does not recognise dual citizenship and have rebuffed all attempts to free her.
Her case has attracted a lot of media coverage and the Foreign Secretary was asked about it when he appeared before a parliamentary select committee last week.
He told MPs: 'When I look at what Nazanin Zaghari-Ratcliffe was doing, she was simply teaching people journalism as I understand it.
'(Neither) Nazanin Zaghari-Ratcliffe nor her family has been informed about what crime she has actually committed. And that I find extraordinary, incredible.'
Mrs Zaghari-Ratcliffe's employers at the Thomson Reuters Foundation have issued an angry