IRAN'S foreign minister has suggested charity worker Nazanin Zaghari-Ratcliffe could be released as part of a prisoner swap.

The British-Iranian mother, whose sister-in-law is a GP in Cwmbran, was sentenced to five years in jail in 2016 after being accused of spying by Tehran's Islamist regime, a charge she vehemently denies.

Javad Zarif said he has the authority to make an "exchange" happen, adding that the United States government knew Iran was prepared to do a swap six months ago.

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Mrs Zaghari-Ratcliffe's husband, Richard Ratcliffe, said he was "surprised" by Mr Zarif's comments and that he would have to speak to the Foreign Office and State Department.

Speaking at the Asia Society, Mr Zarif said: "We have an Iranian lady in Australia who gave birth to a child in prison, not even on bail, inside prison, on an extradition request by the United States because she was responsible as a translator in a, whatever, in a purchase operation - purchase - of some transmission equipment for Iranian broadcasting company.

"That's her charge. She has been lingering in an Australian jail for the past three years. Now we hear about Nazanin Zaghari (Ratcliffe) and her child, and I feel sorry for them and I have done my best to help, but nobody talks about this lady in Australia who gave birth to a child in prison whose child is growing up outside prison with mother in prison.

"So, what can I do as a foreign minister? And I put this offer on the table publicly now. Exchange them.

"All these people that are in prison, inside the United States, on extradition request from the United States - we believe their charges are phoney.

"The United States believes the charges against these people in Iran are phoney. Fine. Let's not discuss that. Let's have an exchange.

"I'm ready to do it. And I have authority to do it. We've informed the government of the United States six months ago that we are ready - not a response yet. If they tell you anything else, they're lying."

Mr Ratcliffe said he is not sure if it is a serious proposal or if it was said as part of a wider context.

"Normally my sense with Iran is nothing is flippant, and so it will have a meaning, but it might not be the obvious meaning," he said.

Richard Ratcliffe. Photo credit should read: Dominic Lipinski/PA Wire

Mr Ratcliffe said in the approximately 40 messages from Iranian authorities about solving Nazanin's case, a prisoner swap was only mentioned once in February 2017.

"Nearly all of those has focused on the outstanding debt that the UK has with Iran," he said.

Mr Ratcliffe said Mr Zarif's suggestion has left him "disoriented", adding that he is "not sure quite what it means".

He said: "It has felt increasingly that we are in the doorway, and we might be held in the doorway for a while, but Nazanin's situation cannot go on for much longer."

Mr Ratcliffe added: "It's always good when we're not forgotten."

Mrs Zaghari-Ratcliffe was arrested with her infant daughter Gabriella on April 3, 2016, at Tehran's Imam Khomeini Airport as she prepared to board a plane back to the UK after visiting relatives.

The 40-year-old is serving a five-year sentence in Tehran's notorious Evin Prison.

The trial by a Revolutionary Court in Tehran was widely condemned as unfair and she strenuously denies the charges against her.

Foreign secretary Jeremy Hunt granted Mrs Zaghari-Ratcliffe diplomatic protection last month.

But Tehran refuses to acknowledge her dual nationality and said the UK's actions were illegal.

Mr Hunt met Mr Zarif last September and wrote on Twitter: "I pressed for swift resolution on all our dual national consular cases, including Nazanin. NOT acceptable to detain innocent people arbitrarily at the cost of enormous human anguish."

Theresa May has also told Iranian President Hassan Rouhani she had "serious concerns" about the jailing of Mrs Zaghari-Ratcliffe.

A Foreign Office spokeswoman said: "The treatment of all British-Iranians detained in Iran, including Mrs Zaghari-Ratcliffe, is a priority for the government.

"We remain concerned about all of our consular cases and raise them at every level and every opportunity."