"The Iranian regime should be in no doubt. We are watching the case of Alireza Akbari closely," he said in a tweet.

Cleverly on Wednesday called for immediate release of Akbari who has been sentenced to death by the Iranian regime on charges of spying for Britain.

Iran's official IRNA news agency published a video on Thursday which it said showed that British-Iranian national Alireza Akbari played a role in the assassination in 2020 of the country's top nuclear scientist, Mohsen Fakhrizadeh.

(Reporting by Akanksha Khushi in Bengaluru; editing by Diane Craft)