A former Iranian defense ministry official, who holds dual Iranian-British citizenship, has been sentenced to death on charges of spying for the UK.

Iranian state media reported Wednesday that Alireza Akbari has been sentenced to death for allegedly spying for MI6.

In a statement published by Iran's Intelligence Ministry, Akbari was described as "one of the most important infiltrators of the country's sensitive and strategic centers".

He was detained more than three years ago and has been in the notorious Evin prison in Tehran since then.

Akbari had been deputy defense minister under the reformist President Mohammad Khatami, from 1997 to 2005. He was also close to Ali Shamkhani, the secretary of the Supreme National Security Council of Iran.

He was an advocate for the Iran nuclear deal known as the JCPOA that was eventually signed in 2015 with world powers.

Britain's Foreign Office has urged the Islamic Republic to immediately release the dual national.

However, Akbari's wife Maryam said an official asked her to visit her husband in jail for a 'final meeting' before his execution.

Reports say he has been moved to solitary confinement, indicating that his execution is imminent.

However, no details have provided about his specific charges and court proceedings.

"Our priority is securing his immediate release and we have reiterated our request for urgent consular access," a UK Foreign Office spokesperson said.

Nournews, which is affiliated to the country's top security agency reported that Akbari's death sentence has been upheld by Iran's Supreme Court.