Boris Johnson is to meet the husband of jailed British mother Nazanin Zaghari-Ratcliffe on Wednesday to discuss the possibility of her being offered "diplomatic protection" as part of Government efforts to secure her return from Iran.
Downing Street confirmed that the Foreign Office is looking into the possible use of the status after Richard Ratcliffe spoke with the Foreign Secretary by phone at the weekend.
It is thought that legal advice will have to be taken before determining whether the status - which would raise Mrs Zaghari-Ratcliffe's plight from a consular case to a formal dispute between the two countries - is the best method for speeding her release.
Mr Johnson returned from Brussels to answer an urgent question on the case in the House of Commons, amid continuing concern that his suggestion to a parliamentary committee that Mrs Zaghari-Ratcliffe was training journalists in Iran has exposed her to the threat of the doubling of her five-year jail sentence.
Boris Johnson's pride "matters not one ounce" compared with Nazanin Zaghari-Ratcliffe's freedom, Labour said, as they urged the British Foreign Secretary to apologise.
Britain's shadow foreign secretary Emily Thornberry said there had been a week of "obfuscation and bluster" from Mr Johnson as she urged him to state "simply and unequivocally" that he got it wrong when claiming Mrs Zaghari-Ratcliffe was training journalists in Iran when arrested in 2016.
The Foreign Secretary, responding to an urgent question in the Commons, said he apologised for the "distress and suffering" caused by his remarks.
He added: "I do apologise, I do apologise and of course I retract any suggestion that she was there in a professional capacity."
Mr Johnson said he had made such a statement about "a dozen times".
Ms Thornberry said Mr Johnson had argued his "training" remark to a Commons committee earlier this month had no connection to threats by the Iranian authorities to extend Mrs Zaghari-Ratcliffe's five-year sentence.
She said that statement has been "entirely contradicted" by the Iranian courts and state television, with all of them saying "explicitly" that the Foreign Secretary's remarks were the "basis of their renewed action" against the mother of one.
Ms Thornberry told the Commons: "We know, from the evidence of Richard Ratcliffe, that when Nazanin was told of the remarks and saw how the Iranian authorities would exploit them she became hugely distressed and upset.
"So will the Foreign Secretary today accept the impact that his words have had, accept the distress that has been caused to Nazanin and apologise properly for that - not apologise for upsetting people, apologise for getting it wrong?"
Ms Thornberry, to cries of "shame" from Labour MPs, also criticised the UK's Environment Secretary Michael Gove for "incredibly" claiming it was not known why Mrs Zaghari-Ratcliffe was in Iran.
She went on: "If it is a matter of pride that the Foreign Secretary is refusing to admit that simply he has made a mistake, well then I feel bound to say to him that his pride matters not one ounce compared to Nazanin's freedom.
"After a week of obfuscation and bluster, will he finally take the opportunity today to state simply and unequivocally for the removal of any doubt - either here or in Tehran - that he simply got it wrong."
Mrs Zaghari-Ratcliffe was arrested and accused of plotting to topple the Iranian regime, which she denies, after being arrested in Tehran last year following a holiday.
Mr Johnson said he would repeat what he said last week, telling MPs: "Yes, of course, I apologise for the distress, the suffering that has been caused by the impression that I gave that the Government believed, that I believed, she was there in a professional capacity.
"She was there on holiday and that is the view."
One Labour MP could be heard saying: "Say sorry."
Mr Johnson continued: "I do apologise, I do apologise, and of course I retract any suggestion that she was there in a professional capacity.
"The honourable members opposite must have heard that from me about a dozen times."
He said he would discuss the idea of giving Mrs Zaghari-Ratcliffe diplomatic protection in a meeting with her husband this week.
Mr Johnson went on: "He has requested to come to Tehran. I don't know whether that will be possible but we will see what we can do."
Responding to Labour's initial question, Mr Johnson earlier outlined the circumstances of Mrs Zaghari-Ratcliffe's arrest before adding the UK Government has "no doubt" she was in Iran on holiday.
He reiterated that his comments to the Foreign Affairs Select Committee should have been clearer, saying: "I acknowledge the words I used were open to being misinterpreted and I apologise to Mrs Zaghari-Ratcliffe and her family if I inadvertently caused them any further anguish."
Some Labour MPs shouted "resign" as Mr Johnson spoke.