Iran's justice ministry confirmed on Friday that authorities have opened a new case against British-Iranian aid worker Nazanin Zaghari-Ratcliffe, who has been sentenced to five years in jail, and denied she might soon be released.

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

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

British foreign minister Boris Johnson travelled to Iran this month to lobby for her release.

‘Iran’s judiciary cannot confirm any of the claims in Western media about this case,’ the head of the justice department in Tehran province, Gholamhossein Esmaili, was quoted as saying by the semi-official Tasnim news agency on Friday.

‘When a decision is made, it will be announced by the Islamic Republic's judiciary or through diplomatic channels,’ he said.

Tasnim said he specifically denied reports of a swap deal, but did not make clear what reports he was referring to.

Zaghari-Ratcliffe's husband Richard Ratcliffe, who called on Iran to release his wife before Christmas, told the Guardian and other British media on Thursday that her lawyer said that her case has been marked as being eligible for early release.

The release of dual national prisoners in Iran in recent years has been mainly done through prisoner swaps.

‘Besides serving her current sentence, she has also another ongoing case against her in court... We do not know if she would be found guilty or not,’ Esmaili said.

His comments mark the first time a justice ministry official has acknowledged that a new case has been brought against Zaghari-Ratcliffe.

Her family said in October that the new case carried charges that could bring mean another 16 years in prison.

The new charges included joining and receiving money from organizations working to overthrow the Islamic Republic and attending a demonstration outside the Iranian Embassy in London, the family said.

Iran refuses to recognise dual nationals and denies them access to consular assistance. It has arrested at least 30 dual nationals during the past two years, mostly on spying charges.