By Victoria Bisset and Katerina Ang 

LONDON — Iran executed Alireza Akbari, a dual British citizen who previously served as a senior defense official in Tehran, in what U.K. Prime Minister Rishi Sunak described as “a callous and cowardly act, carried out by a barbaric regime with no respect for the human rights of their own people.”

Mizan, a news service linked to the Iranian judiciary, said early Saturday that Akbari had been hanged without providing details on when the execution took place. It previously said that Akbari had been sentenced to death for carrying out espionage activities on behalf of MI6, the British foreign intelligence service.

Iran has a history of making unsupported claims of espionage when it makes arrests.

“This will not stand unchallenged,” said British Foreign Secretary James Cleverly in a statement, adding that Britain would summon Tehran’s top diplomat in London “to make clear our disgust at Iran’s actions.”

Britain’s Foreign Office previously said it had lobbied Tehran for Akbari’s release, but was not granted consular access. Iran does not recognize dual citizenship.

U.S. State Department deputy spokesman Vedant Patel on Friday called the Iranian charges “politically motivated” and said that Akbari’s execution would be “unconscionable."

The theocratic regime in Iran has launched a brutal crackdown on demonstrators after a wave of anti-government protests began in September. Tehran has executed at least four people in relation to the protests, while at least 520 demonstrators have been killed, according to the Human Rights Activists News Agency. IranIt has repeatedly made the unsupported claim that Western powers and Israel were behind the demonstrations.

Akbari’s wife told the BBC’s Persian Service earlier this week that he had been taken to solitary confinement and that relatives had been told any visit to Akbari would be his last. She added that he had been detained for over three years.

Akbari, 61, had served as deputy defense minister during the administration of Iran’s President Mohammad Khatami, a pro-reform cleric who was in power between 1997 and 2005. During this time, Akbari served under then-defense minister Ali Shamkhani — now the secretary of Iran’s Supreme National Security Council of Iran and at whose invitation Akbari returned to Iran before he was arrested, Akbari’s brother told BBC Persian.

Akbari also played a role in the cease-fire that ended a bloody eight-year war with Iraq in 1988, according to the Associated Press. He reportedly lived in Britain for over 10 years.

Iranian state media this week broadcast a highly edited video showing Akbari’s alleged confessions, and claimed that Akbari had received more than $2.3 million in return for spying for Britain — after he was initially contacted by British intelligence agents during a visa interview at the embassy in Tehran.

One on-screen caption in the confession video said Akbari had provided information about Mohsen Fakhrizadeh, an Iranian nuclear scientist killed in attack outside Tehran in 2020. In a later section, the video said he had been arrested for spying in 2008 but traveled to Britain after he was released on bail.

Yet the BBC’s Persian Service released a recording it said Akbari made from prison. In it, Akbari says he had been threatened with death if he did not confess.

Akbari said his “will was broken” and he was “driven to the point of insanity” by torture and psychedelic drugs during more than 3,500 hours of interrogations. Iran had “no proof” of the claims against him and had acted to “take revenge” against Britain, he said, adding that he had been accused of obtaining information from Shamkhani “in exchange for a bottle of perfume and a shirt.”

Research published last year, cited by the British parliament, suggests that least 66 foreign or dual nationals have been arrested by Iran since 2010, including around 15 Britons. They include British Iranian Nazanin Zaghari-Ratcliffe, who was freed last year following six years of prison and house arrest in Iran.

In November, Iranian state media reported that another British national, who also holds Iranian citizenship, was arrested on accusations of communicating with foreign news channels, according to Reuters.

Dissidents based abroad have also faced threats in recent years. Jamshid Sharmahd, a German Iranian citizen and California resident in his 60s, was allegedly kidnapped during a flight layover in Dubai in August 2020 and taken to Iran, where he was accused of leading a “terrorist” group — a charge he denies.

His daughter says he faces the death penalty after being accused of “corruption on earth.”

In 2019, Ruhollah Zam, a prominent exiled journalist living in France, was arrested and extradited to Iran after being lured to neighboring Iraq. He, like Akbari, was convicted of “corruption on earth” and was executed in December 2020.

Ang reported from Seoul.