The family of a British-Iranian dual national sentenced to death in Iran have told BBC Persian that authorities are preparing to execute him.
Alireza Akbari's wife, Maryam, said the family had been asked to go to his prison for a "final visit" and that he had been moved to solitary confinement.
The ex-deputy Iranian defence minister was arrested in 2019 and convicted of spying for the UK, which he denied.
The UK urged Iran to halt the planned execution and immediately release him.
"This is a politically motivated act by a barbaric regime that has total disregard for human life," Foreign Secretary James Cleverly tweeted.
Earlier, a Foreign Office spokesperson told the BBC that it was supporting Mr Akbari's family and had repeatedly raised his case with Iranian authorities.
It has requested urgent consular access, but Iran's government does not recognise dual nationality for Iranians.
BBC Persian also broadcast an audio message on Wednesday from Mr Akbari in which he says he was tortured and forced to confess on camera to crimes he did not commit.
He says that he was living abroad a few years ago when he was invited to visit Iran at the request of a top Iranian diplomat who was involved in nuclear talks with world powers.
Once there, he adds, he was accused of obtaining top secret intelligence from the secretary of Iran's Supreme National Security Council, Ali Shamkhani, "in exchange for a bottle of perfume and a shirt".
Mr Akbari served under Mr Shamkhani when the latter was defence minister during the presidency of Mohammad Khatami, a reformist who was in office for two terms between 1997 and 2005.
“I was charged with obtaining top secret intelligence from Iran’s head of National Security Council in exchange for a bottle of perfume & a shirt during Rouhani’s administration,” Alireza Akbari said in an audio file obtained by BBC Persian.
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Mr Akbari alleges in the audio message that he was "interrogated and tortured" by intelligence agents "for more than 3,500 hours".
"During all those 3,500 hours, which took more than 10 months, they were recording my confessions with 10 cameras to make their Hollywood-style film," he says, adding that he was also given "psychedelic drugs".
"By using physiological and psychological methods, they broke my will, drove me to madness and forced me to do whatever they wanted. By the force of gun and death threats they made me confess to false and corrupt claims."
He also accuses Iran of seeking "to take revenge on the UK by executing me".
Hours after the audio message was broadcast, the Iranian judiciary's Mizan news agency confirmed for the first time that Mr Akbari had been found guilty of espionage, and that the Supreme Court had rejected his appeal.
It cited Iran's intelligence ministry as saying that Mr Akbari had been "one of the most important infiltrators of the country's sensitive and strategic centres" for the UK's Secret Intelligence Service, better known as MI6, and that he had been "compiling and consciously transferring sensitive information".
The ministry claimed that its agents uncovered Mr Akbari's spying by feeding him false information.
At the end of November, Iranian state media reported that authorities had hanged four men convicted of "co-operating" with Israeli intelligence.
Four other men have been executed since December after being sentenced to death in connection with the anti-government protests engulfing the country.
Alicia Kearns, chair of the UK House of Commons Foreign Affairs Committee, said the news from Mr Akbari's family was "awful".
"Unfortunately, it is another horrifying example of the Iranian regime – because they feel they are cornered, because there is such significant pressure from sanctions on them – weaponising British nationals and industrialising hostage taking," she told BBC Radio 4's PM programme.
She speculated that Mr Akbari might have been singled out by hard-liners in the establishment in order to undermine Mr Shamkhani, who she described as a "moderate voice… [who] has been calling for discussions and dialogue" in response to the current protests. Iran's current leaders have portrayed them as "riots" and cracked down on them with lethal force.
Iran has arrested dozens of Iranians with dual nationality or foreign permanent residency in recent years, mostly on spying and national security charges.
British-Iranian citizens Nazanin Zaghari-Ratcliffe and Anoosheh Ashoori were released and allowed to leave Iran last year after the UK settled a long-standing debt owed to Iran.
However, at least two other British-Iranians remain in detention beside Mr Akbari, including Morad Tahbaz, who also holds US citizenship.
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