LONDON (Reuters) - A British-Iranian aid worker who has been jailed in Tehran is going on hunger strike in protest at her treatment, her employer and her husband said.

Nazanin Zaghari-Ratcliffe, 40, 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 to five years in jail 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.

“Nazanin called me this morning to confirm from Evin prison that she has started this hunger strike this morning. It is initially a three-day hunger strike,” her husband, Richard Ratcliffe, said.

He said Nazanin was taking the action to press demands for access to specialist doctors to address health concerns and to be allowed such treatment as they prescribed.

A spokesman for Iran’s judiciary declined to comment.

Britain has said it will not let Zaghari-Ratcliffe’s case rest and Foreign Secretary Jeremy Hunt said he had summoned Iran’s ambassador on Monday to demand she had immediate access to the healthcare she needed.

“Her ongoing detention is TOTALLY unacceptable and her treatment at the hands of Iranian authorities is a fundamental breach of human rights,” Hunt wrote on Twitter.

Iran said Britain’s intervention was an interference in its affairs and was unacceptable, state news agency IRNA reported.

“Mrs. Zaghari, as an Iranian national, has received necessary medical care in prison and she will continue to enjoy her right to access the medical care while in jail,” IRNA quoted Iran’s ambassador to Britain, Hamid Baeidinejad, as saying.

Iran has said that the trial and the verdict are in the hands of the judiciary.

Monique Villa, CEO of the Thomson Reuters Foundation, said it was “extremely shocking to see our colleague...going on hunger strike to protest at her inhumane treatment.”

Britain has advised British-Iranian dual nationals against all but essential travel to Iran, tightening its existing travel advice and warning it has only limited powers to support them if detained.