Boris Johnson has admitted feeling a "deep sense of anguish" over the case of Nazanin Zaghari-Ratcliffe.
The former Foreign Secretary said he feels “sorry” for the jailed British-Iranian charity worker but rejected responsibility for her plight, saying it lies with the Iranian Revolutionary Guard.
Mr Johnson has come under fire for remarks he made in 2017 while Foreign Secretary in which he said Ms Zaghari-Ratcliffe was teaching people journalism.
The 40-year-old was arrested at Tehran's Imam Khomeini airport while travelling with her young daughter in April 2016 and was accused of spying.
She denied the charge but was sentenced to five years in prison.
Appearing on Sky News' Sophy Ridge on Sunday, Tory leadership hopeful Mr Johnson said: "I feel sorry for her, for her daughter, for her husband Richard and I've said this many, many times.
“I feel a deep sense of anguish for what she has been going through."
Mr Johnson added: "When it comes to responsibility for what she is suffering I think that is incredibly important that we in the UK do not unwittingly give aid and succour to the people who are really responsible, which is not the Foreign Office, not the former foreign secretary, and no-one in London is responsible for incarcerating Nazanin Zaghari-Ratcliffe.
"The people who are responsible are the Iranian Revolutionary Guard, and anything you do to exculpate them is, I think, a great shame."
Ms Zaghari-Ratcliffe and her husband, who is protesting outside the Iranian Embassy in London, have both been on hunger strikes in protest at her “unfair imprisonment”.
Mr Ratcliffe said his wife had decided to end her 15-day hunger strike and had eaten some porridge with apple and banana.
It was put to Mr Johnson that Mr Ratcliffe believes his words had ‘traumatic’ effects for his wife.
Mr Johnson replied: "I do feel a deep sense of anguish about it as I have said and I have apologised several times in the House of Commons and elsewhere.
"But it is very very important that in this conversation we don't allow whatever I may have said or done to cloud the issue."
He repeated his criticism of the Iranian Revolutionary Guard and urged them to release Ms Zaghari-Ratcliffe and others.
Conservative former cabinet minister Sir Patrick McLoughlin, a supporter of Jeremy Hunt as the next Tory leader, said Mr Johnson's language had "not helped" Ms Zaghari-Ratcliffe's case.
Speaking on the same programme as Mr Johnson, he said: "Obviously Iran is responsible for holding somebody in their jail and somebody that should be released as soon as possible.
"I think everybody has great sympathy with her family... I think some of the language that Boris has used has not helped her case."