Iranian-British aid worker Nazanin Zaghari-Ratcliffe is seen in an undated photograph handed out by her family. Photo: Ratcliffe Family Handout via Reuters.

Jailed British-Iranian aid worker Nazanin Zaghari-Ratcliffe will serve out her five-year prison sentence, Iran’s Foreign Ministry spokesman said on Monday, dismissing a call for her release by a British minister visiting Tehran.

“Mrs Zaghari is an Iranian. She has been convicted on security charges and is spending her sentence in prison,” Iranian Foreign Ministry Spokesman, Abbas Mousavi, was quoted as saying by the state media.

“Iran does not recognize dual nationality,” he said.

Foreign Office minister Andrew Murrison pressed Iran for the “urgent and unconditional release” of Zaghari-Ratcliffe on Sunday, during a visit to Iran to discuss the situation in the Middle East, his ministerial area of responsibility.

Fears of a direct military confrontation between Washington and Tehran have risen sharply since Iran shot down a US drone last week and US President Donald Trump called off a retaliatory strike while bombers were in the air.

Zaghari-Ratcliffe, a project manager with the Thomson Reuters Foundation, was arrested in April 2016 at a Tehran airport as she headed back to Britain with her daughter after a family visit.

She was sentenced after being convicted of plotting to overthrow Iran’s clerical establishment, a charge denied by her family and the Foundation, a charity organization that operates independently of Thomson Reuters and Reuters News.

Zaghari-Ratcliffe’s husband Richard started a hunger strike outside the Iranian Embassy in London last week to draw attention to his wife’s plight.

“We do not approve such measures.. They are against international conventions,” Mousavi said in the statement. “If someone has a request, we advise them follow it through legal channels and let the Iranian embassy do its work.”

Ratcliffe did not immediately respond to attempts by Reuters to contact him for a response to Mousavi’s comments.