The Nation- Iran has stepped back from an offer to exchang the British-Iranian prisoner Nazanin Zaghari-Ratcliffe for an Iranian woman being held in Australia.

Iranian Foreign Minister Mohammad Javad Zarif on Wednesday suggested a swap between Nazanin Zaghari-Ratcliffe, who is in jail in Tehran on claims of sedition, and Negar Ghodskani, an Iranian woman detained in Australia on a US extradition warrant.

But on Thursday he rescinded the offer, saying Ms Zaghari-Ratcliffe�s case could not be considered in a prisoner swap. It was a �separate case�.

British Foreign Secretary Jeremy Hunt had earlier dismissed the suggestion of a prisoner swap for the British mother as a "vile" diplomatic ploy and said there was a "huge difference" between the two women.

"The woman in jail in Australia is facing due process, a proper legal procedure, and she is alleged to have committed a very serious crime," Mr Hunt said.

"Nazanin Zaghari-Ratcliffe is innocent. She has done nothing wrong.

"What is unacceptable about what Iran is doing is that they are putting innocent people in prison and using it as leverage.

"They're saying, 'We'll only release this innocent Brit if you'll do something that suits us diplomatically'."

Richard Ratcliffe, Ms Zaghari-Ratcliffe's husband who has been campaigning for her release, said he was "blindsided" by the offer as he followed Mr Zarif's speech on Twitter.

He said he did not think was is the "way forward".

"It's clearly a hopeful thing that he was talking about her release explicitly," Mr Ratcliffe said.

"At the same time, linking her in a public way to a big, complicated deal that is almost impossible to do because it's been made public could easily be a displacement tactic."