The Mayor of London, Sadiq Khan, is the latest official to call on UK Foreign Secretary Boris Johnson to resign.

Khan said Johnson should leave office after a series of gaffes that offended several people including Libyans and Americans.

Johnson is facing mounting pressure to leave office after he made some damaging remarks on the case of a British national held in Iran.

The Foreign Secretary incorrectly stated that Nazanin Zaghari-Ratcliffe, a charity worker and a project manager with the Thomson Reuters Foundation (TRF), was "simply teaching people journalism" in Iran when she was arrested in 2016. The 38-year-old mother from London was sentenced to five years in prison after being accused of leading a "soft coup".

Johnson was criticised for incorrectly stating that Zaghari-Ratcliffe was in the country in a working capacity. Both TRF and Zaghari-Ratcliffe's husband, Richard, maintain that the woman was on holiday at the time of her arrest – a central part of her defence .

"This is the latest on along list of gaffes made by our Foreign Secretary," Khan told the BBC Andrew Marr show.

"I think he's got to go. If Theresa May was a strong Prime Minister, she would have sacked him a long time ago."

Khans' comments came just hours after Labour Party leader Jeremy Corbyn urged May to sack Johnson following his "deeply regrettable error" on the Iran case.

MPs including Conservative's Anna Soubry, Labour's Yvette Cooper and Green Party's Caroline Lucas also called on Johnson to leave office.

In October 2016, Johnson stirred criticism for claiming that if Libya cleared away dead bodies, it could turn Sirte into the next Dubai. He also said previous US President Barack Obama was anti-British because he was partly Kenyan

Nazanin Zaghari-Ratcliffe's sentence could be doubled

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Iran exploited Johnson's comments in court as offering new evidence against Zaghari-Ratcliffe and why she was in the Islamic Republic at the time of her arrest. She was accused of engaging in "propaganda against the regime" and could face an additional five-year sentence.

In spite of calls to do so, Johnson did not fully backtrack on his comments, nor did he apologise. However, he admitted he could have been "clearer" and suggested he goes to Iran by the end of the year to further discuss the case.

Foreign Office full statement:

"The Foreign Secretary called the Iranian Foreign Minister Javad Zarif this morning to discuss the case of Mrs Nazanin Zaghari Ratcliffe. He reiterated his anxiety about the continued suffering of Mrs Zaghari Ratcliffe and her family, and hoped a solution would be reached soon.

"The Foreign Secretary expressed concern at the suggestion from the Iranian Judiciary High Council for Human Rights that his remarks last week at the Foreign Affairs Committee 'shed new light' on the case. The Foreign Secretary said this was absolutely not true. It was clear, as it always had been, that Mrs Zaghari Ratcliffe had been in Iran on holiday when arrested.

"The Foreign Secretary made clear that the point he had been seeking to make in his evidence to the FAC was that he condemned the Iranian view that training journalists was a crime, not that he believed Iranian allegations that Mrs Zaghari Ratcliffe had been engaged in such activity.

"The Foreign Secretary concluded by emphasising that his remarks could form no justifiable basis for further action in this case and urged the Iranian authorities to release Mrs Zaghari Ratcliffe on humanitarian grounds. He set out his intention to visit Iran before the end of the year to discuss the case further.

"Mr Zarif said that the developments in the case over the weekend were unrelated to the Foreign Secretary's remarks and that he remained committed to working with the Foreign Secretary to finding a resolution to the case on humanitarian grounds.

"The Foreign Secretary accepts his remarks to the Foreign Affairs Committee could have been clearer on this aspect. He intends to update the House this afternoon."