The Foreign Office said that Johnson telephoned his Iran foreign minister, Javad Zarif, on Tuesday morning to discuss the case of Zaghari-Ratcliffe, who was arrested while visiting the country with her young daughter past year.
As Henry Ridgwell reports, Iran has already picked up on Boris Johnson's comments to justify its actions.
"I think it is important we keep this in perspective ... the point the Foreign Secretary was making was that this arrest and detention of a United Kingdom citizen is not acceptable", he added.
Her employer, the Thomson Reuters Foundation have demanded Mr Johnson "immediately correct the serious mistake he made", explaining that Mrs Zaghari-Ratcliffe is a project manager for the charity and has never trained journalists.
He said he was concerned at suggestions from Tehran that his remarks last week to the Foreign Affairs Select Committee were being used as justification to increase Ms Zaghari-Ratcliffe's jail term.
"[Neither] Nazanin Zaghari-Ratcliffe nor her family has been informed about what crime she has actually committed".
He told the parliamentary committee on November 1: 'When I look at what Nazanin Zaghari-Ratcliffe was doing, she was simply teaching people journalism, as I understand it, at the very limit'.
A U.K. Foreign Office statement said Johnson accepted his remarks to the Foreign Affairs Committee "could have been clearer on this aspect".
Four days later, she was summoned before a court and told Mr Johnson's comments were proof that she was engaged in "propaganda against the regime".
The Foreign Secretary now faces criticism he has harmed her defence.
Last week, Johnson told a British Parliament committee that Zaghari-Ratcliffe, who was detained at Tehran airport along with her young daughter in April 2016, had been teaching journalism during her visit.
"It was clear, as it always had been, that Mrs Zaghari Ratcliffe had been in Iran on holiday when arrested", the statement said.
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Boris Johnson has falsely claimed a British-Iranian mother being held in Iran jail was in the country training journalists.
"The UK Government has no doubt that she was on holiday in Iran when she was arrested previous year and that was the sole objective of her visit".
Zaghari-Ratcliffe was jailed for five years on espionage charges after her arrest last year.
Johnson will travel to Iran before the end of the year to discuss the matter further, the Foreign Office said.
"I see a direct correlation between this statement by Boris Johnson, who rightly condemned the treatment that Nazanin has received in Iran, and the fact that Nazanin was brought once again into court", she said.
Zaghari-Ratcliffe is now being held in Iran for allegedly trying to overthrow the government, despite being on holiday and not working as a journalist during her time in the country.
In October, when the new charges were filed, husband Richard Ratcliffe said the British government should be doing more to help his wife, and that it should not be making business deals with the regime that has imprisoned her.
"The UK Government has no doubt that she was on holiday in Iran when she was arrested a year ago and that was the sole objective of her visit. And that I find extraordinary, incredible".
The Iranian government accused her of working for a United Kingdom media network involved in activities against Iran.
On Saturday, she faced Abolghassem Salavati, a notoriously harsh judge who sentenced her in the first trial.
The CEO of Thomas Reuters Foundation, where Nazanin worked, Monique Villa has also called for the Foreign Secretary to retract his comments.
Shadow foreign secretary Emily Thornberry told the minister he should "engage his brain" and apologise for his "foolish words", and called on him to resign. Iranian prosecutor Abbas Jafari Dolatabadi said the letter demonstrated Zaghari-Ratcliffe's importance to the British authorities, but he did not say when it was sent or provide any other details about it.