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Input: London (CNN) Britain's beleaguered Prime Minister Theresa May has been urged to sack  her Foreign Secretary Boris Johnson  over his handling of the Nazanin Zaghari-Ratcliffe case.
On Sunday both Labour leader Jeremy Corbyn and London Mayor Sadiq Khan called on May to fire  Johnson -- who has been under increasing pressure since Iranian state TV claimed that his statements on the plight of the British-Iranian woman imprisoned in Tehran on charges of espionage confirmed her guilt .
Writing in the Observer on Sunday  Corbyn took aim at  Johnson   calling for him to be relieved of his duties after "undermining our country" and "putting our citizens at risk."
Also on Sunday  the UK Foreign Office told CNN that  Johnson  had held a "constructive" conversation with Richard Ratcliffe  the husband of Zaghari-Ratcliffe.
 Johnson  has been on the defensive over the past week since being forced to correct remarks  he  made to a British parliamentary committee  when  he  said that Zaghari-Ratcliffe  who has been in jail since she was detained at Tehran airport in April 2016  had been teaching journalism during her visit to the country. Zaghari-Ratcliffe and her family have maintained that she was in Iran visiting family.
After  Johnson 's original comments  authorities in Iran filed further charges against Zaghari-Ratcliffe  prompting fears her five-year sentence could be extended. On Wednesday  Iranian state TV IRIB said  Johnson  amounted to an unintentional confession.
 Foreign Secretary Boris Johnson  is set to visit Iran before the end of the year.
In  his  article  Corbyn says that the "heartbreaking" case of Zaghari-Ratcliffe has left her future liberty in peril because of  Johnson 's "serial bungling."
In a blunt final paragraph  Corbyn added: "We've put up with him embarrassing and undermining our country through his incompetence and putting our citizens at risk for long enough. It's time for  Boris Johnson  to go."
Khan was similarly critical of  Johnson   his predecessor as mayor of London calling on him to "clarify the huge error he made" and help bring Zaghari-Ratcliffe back to the UK.

Theresa May urged to fire Boris Johnson by top UK politicians