Video report by ITV News Political Correspondent Romilly Weeks
Boris Johnson has accepted he "could have been clearer" when making comments that Tehran reportedly used to justify extending the jail sentence of a British woman being held in Iran.
But in a telephone call with his Iranian counterpart Javad Zarif on Tuesday, Mr Johnson said his comments provide "no justifiable basis" for further legal action against Nazanin Zaghari-Ratcliffe.
Last week, the Foreign Secretary told a parliamentary committee that Mrs Zaghari-Ratcliffe was training journalists in Iran when she was arrested last year.
Her employer and her family have insisted this is incorrect and urged Mr Johnson to retract his claim, while there have also been calls for him to quit as a result.
Mrs Zaghari-Ratcliffe, who is serving a five-year sentence in an Iranian jail, was summoned to an unscheduled court hearing last weekend at which Mr Johnson's remarks were cited as proof that she had been engaged in "propaganda against the regime".
Reports suggest the new charge could add five years to her prison term, imposed over unspecified allegations of involvement in a supposed coup attempt against the Tehran regime, which she denies
Mr Zarif said that the developments in the case over the weekend "were unrelated to the Foreign Secretary's remarks".
Speaking in the Commons later on Tuesday, Mr Johnson refused to apologise when asked by Emily Thornberry and accused her of "point-scoring" instead.
He said: "I also voiced my concern at the suggestion emanating from one branch of the Iranian judiciary that my remarks to the Foreign Affairs Select Committee last week had some bearing on Ms Zaghari-Ratcliffe's case.
"The UK Government has no doubt that she was on holiday in Iran when she was arrested last year and that was the sole purpose of her visit.
"My point was that I disagreed with the Iranian view that training journalists was a crime - not that I wanted to lend any credence to Iranian allegations that Ms Zaghari-Ratcliffe has been engaged in such activity.
"I accept that my remarks could have been clearer in that respect and I'm glad to provide this clarification."
Mr Johnson said he will discuss all the UK's consular cases when he visits Iran in the coming weeks.
In his call to Mr Zarif, the Foreign Secretary "reiterated his anxiety about the continued suffering of Mrs Zaghari-Ratcliffe" and "expressed concern" that his comments may have "shed new light" on the case.
"The Foreign Secretary said this was absolutely not true," a Foreign Office spokesperson said. "It was clear, as it always had been, that Mrs Zaghari-Ratcliffe had been in Iran on holiday when arrested.
“The Foreign Secretary made clear that the point he had been seeking to make in his evidence to the FAC was that he condemned the Iranian view that training journalists was a crime, not that he believed Iranian allegations that Mrs Zaghari-Ratcliffe had been engaged in such activity.
"The Foreign Secretary concluded by emphasising that his remarks could form no justifiable basis for further action in this case and urged the Iranian authorities to release Mrs Zaghari-Ratcliffe on humanitarian grounds."
Mr Johnson plans to visit Iran before the end of the year, when he will discuss the case further.
Ms Zaghari-Ratcliffe insisted in her original trial that she was not working in Iran at the time of her arrest, but was visiting the country to show her infant daughter Gabriella to her grandparents.
Mr Johnson told a 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.
"(Neither) Nazanin Zaghari-Ratcliffe nor her family has been informed about what crime she has actually committed. And that I find extraordinary, incredible."
Following Saturday's hearing, the Iranian judiciary's High Council for Human Rights said: "His statement shows that Nazanin had visited the country for anything but a holiday.
"For months it was claimed that Nazanin is a British-Iranian charity worker who went to see her family when she was arrested...Mr Johnson's statement has shed new light on the realities about Nazanin."
Ms Zaghari-Ratcliffe's employer, Thomson Reuters Foundation, urged Mr Johnson to correct his "serious mistake", while her husband, Richard Ratcliffe, Mr Johnson should make a statement in Parliament to correct his mistake.
Shadow foreign secretary Emily Thornberry said Mr Johnson should quit if his actions have damaged Ms Zaghari-Ratcliffe's prospects of freedom.
In a letter to the Foreign Secretary, Ms Thornberry said that although Mr Johnson's comment was not a deliberate error, it "reveals a fundamental lack of interest or concern for the details of Nazanin's case and the consequences of your words".
Downing Street said Theresa May still had "full confidence" in her Foreign Secretary.