Jeremy Hunt has admitted he felt he had let down Nazanin Zaghari-Ratcliffe, the British mum held in Iran, every day she remains in prison.
He was asked to talk about the last time he let someone down during a Tory leadership hustings in Darlington.
He paused before answering the question - but his answer had a link to his leadership rival Boris Johnson .
Mr Hunt said: “I feel like I’m letting down Nazanin Zaghari-Ratcliffe every single day that she remains in jail while I’m Foreign Secretary.
“I’ve tried very hard to get her out, I’ve met her husband Richard Ratcliffe on several occasions, she has a daughter the same age as my daughter. And it’s a very big deal.”
The British-Iranian mother is currently jailed in Tehran on spying charges.
Her sentence was increased after Mr Johnson, while he was Foreign Secretary said, said she was "teaching people journalism" in Iran rather than visiting her family.
But he has repeatedly rejected suggestions he is to blame for her continued incarceration.
Asked about his comments last week, Mr Johnson bizarrely appeared to accuse Sky News' Sophy Ridge of giving "succour to the people who are really responsible".
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."
He 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."
The mum of one was arrested at Tehran airport in April 2016 and sentenced to five years in jail after being accused of espionage.
