The Mizan News Agency, affiliated with the Iranian Judiciary, reported on Saturday Tehran has executed Akbari who was sentenced to death over long-running espionage for MI6.
Sunak has called it a “cowardly act, carried out by a barbaric regime with no respect for the human rights of their own people”.
Sunak, writing on Twitter, said: “I am appalled by the execution of British-Iranian citizen Alireza Akbari in Iran.
“My thoughts are with Alireza’s friends and family,” he added.
Cleverly also said it would not go unchallenged.
“This barbaric act deserves condemnation in the strongest possible terms,” he stated, adding, “This will not stand unchallenged.”
Akbari was a former Iranian deputy defense minister who had lived in the UK for more than a decade. He had been arrested over three years ago.
He had been found guilty of “corruption on earth and extensive action against the country’s internal and external security through espionage for the British government’s intelligence service”, according to a report.
The ex-official had received 1,805,000 euros, 265,000 pounds, and 50,000 dollars for spying, it added.
Among other crimes, Akbari is said to have played a role in the assassination by Israel of Mohsen Fakhrizadeh, a top nuclear scientist, in 2020.