The Thomson Reuters Foundation, a British charity group, said on Monday that inaccurate comments made by Johnson about imprisoned aid worker Nazanin Zaghari-Ratcliffe had been cited as proof by the Iranian courts in a bid to prolong her sentence.

The UK foreign secretary told a parliamentary enquiry last week that Zaghari-Ratcliffe had been in Iran last year "simply teaching people journalism as I understand it" before she was arrested at Tehran airport and sentenced to five years in prison for allegedly plotting the "soft toppling" of Iran's regime.

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Zaghari-Ratcliffe's employer, Thomson Reuters Foundation, dismissed Johnson's comments, saying that she had never worked as a journalist and that she was in Iran to take her toddler daughter to visit relatives. "She is not a journalist and has never trained journalists at the Thomson Reuters Foundation where she is project manager in my Media Development team," the foundation's chief executive, Monique Villa, said in a statement. The Thomson Reuters Foundation is an independent entity from Reuters' news arm.

However, Following Johnson's remarks, Zaghari-Ratcliffe was reportedly summoned to an unscheduled court hearing, where the foreign secretary's remarks were cited as evidence by the judge that the British-Iranian aid worker "had visited the country for anything but a holiday.

"I see a direct correlation between this statement by Boris Johnson, who rightly condemned the treatment that Nazanin has received in Iran, and the fact that Nazanin was brought once again into Court on Saturday 4 November," Villa added. She urged the UK's top diplomat to retract the statement, saying it "can only worsen her sentence."

Read more: Iran's judiciary accuses British-Iranian woman of bid to 'overthrow' government

Whitehall offers no clarification or retraction

The Foreign Office, however, refused to clarify or retract Johnson's comments, saying in a statement that his words "provide no justifiable basis on which to bring any additional charges against Nazanin Zaghari-Ratcliffe."

It said Johnson discussed the matter with Iran's Foreign Minister, "to raise again his serious concerns about the case and ensure his remarks are not misrepresented."

"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," the Foreign Office said.

However, Tulip Siddiq, a lawmaker for the opposition Labour Party, accused Johnson of undermining efforts to secure the aid worker's release, calling the foreign secretary's comments "untrue and unhelpful" and his failure to retract the comments as "unforgivable."

Zaghari-Ratcliffe's family and employers deny the charges.

dm/kl (Reuters, AP)