Boris Johnson has sidestepped questions about the future of jailed British woman Nazanin Zaghari-Ratcliffe after Iranian state TV reported that he had made an “unintended confession” that she was training journalists.

The Foreign Secretary is facing calls to step down over his mistaken comments – made to MPs last week – amid fears the Iranian authorities have taken the claims as a justification for her continued imprisonment.

Iran’s state broadcaster said his remarks were “proof” of the accusations against the mother-of-one, who was detained in Tehran on spying charges while on holiday 18 months ago.

Mr Johnson refused to refer to Ms Zaghari-Ratcliffe by name when ambushed by reporters in Washington, saying that his department had “some difficult cases” it was working on in Iran.

It comes as her husband Richard Ratcliffe described the devastating impact of her detainment on the family, as the couple’s young daughter Gabriella, now 3, remains with her grandparents in Tehran after her mother’s arrest.

Mr Johnson sidestepped questions over whether he was “unsackable”, saying he had made “very good progress” in meetings in Washington on the future of Iran nuclear deal. 

He told Sky News: “The crucial thing is that here in Washington they are very sceptical about Iran, you saw what the President had to say but we think there is great value in that nuclear deal.

“We think it’s worth a great deal of energy and effort, to try to keep alive that basic symmetry of stopping the Iranians from acquiring nuclear weapons in exchange for some economic progress.”

Pressed on Ms Zaghari-Ratcliffe’s future, he said: “We have some difficult consular cases in Iran and we are working on all of them.”

The 38-year-old charity worker was separated from her young daughter Gabriella when she was arrested as she tried to return home to London in April 2016.

Gabriella, now three, remains in Iran with Nazanin’s parents, while her mother is in a high-security prison and her father Richard is in London.

A statement from the Free Nazanin Campaign said: “Nazanin’s parents watched the main evening news in growing horror last night. They remain in a state of shock and disbelief.

“As the news stories unfolded from Iranian state media… Nazanin’s father tried to call her lawyer, and eventually spoke to him late at night – to ask what was going on, what did this mean.

“Her lawyer was unable to calm him. Following the news Nazanin’s mother was too distressed to complete cooking the family meal and was unable to speak to anyone for a number of hours.”

Mr Johnson faced calls to resign over the blunder but he refused to apologise, using a statement in the Commons to clarify the remarks and to say there was “no connection” between his comments and fresh charges levelled against Ms Zaghari-Ratcliffe.