Nazanin Zaghari-Ratcliffe's husband admits he 'resented' Boris Johnson's handling of her case
Richard Ratcliffe, who has joined his wife on hunger strike to protest her continued detention, said Johnson "made a promise that he wasn't able to deliver on", in comments to the BBC's Andrew Marr Show.
"He clearly made a mistake and clearly tried to correct it," he added.
Zaghari-Ratcliffe, who worked for the charity arm of news agency Thomson Reuters, was arrested in April 2016 on charges of plotting against the Iranian government. Her family denies the allegations.
Johnson in 2017 said Zaghari-Ratcliffe was working in Tehran to train journalists - comments that were later used to bolster Iran's allegations that she was engaged in "propaganda against the regime".
Ratcliffe protested outside the Iranian embassy in London on Sunday. He said he will continue to "amplify her message".
He and his family will try to "push" the new Foreign Secretary Jeremy Hunt into putting added pressure on Iran.
"I had a chat with the Foreign Secretary yesterday, it felt like there were sort of mixed signals coming out of Iran," he said.
Jailed for over three years, Nazanin-Ratcliffe will refuse food but continue drinking water until she is granted "unconditional release".
Zaghari-Ratcliffe previously went on hunger strike in January.
Zaghari-Ratcliffe wrote an emotional letter to her five-year-old daughter to mark the occasion of her fifth birthday.
The letter, published by The Mirror, revealed that Zaghari-Ratcliffe's daughter Gabriella asked to celebrate her fifth birthday in prison with her mother.
Ratcliffe said his wife "had vowed that if we passed (daughter) Gabriella's fifth birthday with her still inside, then she would do something - to mark to both governments that enough is enough. This really has gone on too long".
Her daughter has resided with her maternal grandparents in Tehran since the arrest.
High-level diplomatic attempts to secure her release have so far failed. Foreign Secretary Jeremy Hunt granted 40-year-old Zaghari-Ratcliffe diplomatic protection in March, but Iranian officials refuse to recognise her dual nationality.
The hunger strike comes amid heightened tensions between the West and Iran, which the US and UK blame for attacks on two oil tankers in the Gulf of Oman this week. Iran denies involvement.
Agencies contributed to this report.
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