A British-Iranian woman jailed in Iran's capital, Tehran, for more than two years is going on a hunger strike in protest of her treatment, her husband has said.

Richard Ratcliffe, the husband of 40-year-old Nazanin Zaghari-Ratcliffe, announced the move on Monday at a press conference held in London.

"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," Ratcliffe said.

He said Nazanin was taking the action to protest against prison officials, who have refused to provide her access to specialist doctors to address concerns over severe neck pains and numbness in her arms and legs.

The strike could be extended if she fails to win assurances of proper medical attention, he added.

A spokesperson for Iran's judiciary declined to comment on the issue, the Reuters news agency reported.

'A breach of human rights'

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

She was subsequently sentenced to five years in jail after being convicted of plotting to overthrow Iran's government, a charge denied by her family and the Foundation, a charity organisation that operates independently of Thomson Reuters and the Reuters news agency.

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.

"We all have Nazanin high in our thoughts as she starts her hunger strike today. It is a truly terrible indictment of Iran's approach that she feels she needs to resort to such an ordeal. Iran must take action now," Hunt said in a series of Tweets.

Today I summoned the Iranian Ambassador to demand Nazanin has immediate access to the healthcare she requires. Her ongoing detention is TOTALLY unacceptable and her treatment at the hands of Iranian authorities is a fundamental breach of human rights 1/2 — Jeremy Hunt (@Jeremy_Hunt) January 14, 2019

Iran, meanwhile, 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.

Dual national arrests

Zaghari-Ratcliffe was released from Tehran's Evin Prison for three days in August last year and reunited with family members, including her four-year-old daughter.

The temporary release came three months after the 40-year-old was summoned to court without a lawyer present under a new charge of "spreading propaganda" against the government.

During the hearing, she was reportedly warned of an additional conviction and an extended jail sentence.

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 arrested.

According to Human Rights Watch (HRW), Iran has arrested several dual nationals who have travelled to the country in recent years.