The husband of a British-Iranian detained by Iran is urging Britain's foreign secretary to publicly correct a statement about his wife, saying the remarks prompted authorities in Tehran to threaten to double her prison sentence.

Nazanin Zaghari-Ratcliffe is serving a five-year sentence for plotting the "soft toppling" of Iran's government.

British Foreign Secretary Boris Johnson told lawmakers last week that Zaghari-Ratcliffe was "simply teaching people journalism" when she was detained last year. Zaghari-Ratcliffe's family and her employer, the Thomson Reuters Foundation, insist she was merely visiting her family.

Richard Ratcliffe told Sky News that Zaghari-Ratcliffe was summoned to an unscheduled hearing, where Johnson's comments were cited as proof that she was engaged in propaganda against the regime.

Ratcliffe urged Johnson on Tuesday to correct his remarks and win Zaghari-Ratcliffe's freedom.