Hillary Clinton used her private email server to discuss details of the Iranian nuclear scientist who has executed for giving information to the CIA.

Shahram Amiri, who was hanged on Sunday for 'revealing secrets to the enemy', was in the US and allegedly informing on Tehran's extensive nuclear program during the Democrat's controversial reign as Secretary of State.

At the time she stressed researcher had been there of his 'own free will' and was described as 'our friend' in correspondences.

But he maintained he had been kidnapped by intelligence agents.

Emails sent by Clinton's advisers point to the scandal involving Amiri - suggesting it was a 'diplomatic, psychological issue', but not a 'legal one'.

One aide also warned he would lead to 'problematic news stories'.

Iranian nuclear scientist Shahram Amiri, who was accused of giving information to the CIA, has been executed

Richard Morningstar, a former State Department special envoy for Eurasian energy wrote to Clinton: 'We should recognize his concerns and frame it in terms of a misunderstanding with no malevolent intent and that we will make sure there is no recurrence.

'Our friend has to be given a way out. Our person won't be able to do anything anyway. If he has to leave so be it.'

Senior adviser Jake Sullivan sent another email about Amiri on July 12, 2010.

It appears he is referring to the scientist just hours before he showed up at the Iranian interests section of the Pakistani Embassy in Washington D.C., demanding he be sent home.

He said: 'The gentleman... has apparently gone to his country's interests section because he is unhappy with how much time it has taken to facilitate his departure.

'This could lead to problematic news stories in the next 24 hours.'

Hillary Clinton used her private email server to discuss details of the Iranian nuclear scientist while he was in the United States

Amiri went missing in 2009 after leaving for a pilgrimage to Mecca, but appeared in a video - apparently recorded in the U.S. - in which he claimed to have been put under pressure to 'reveal sensitive information' to the intelligence agency.

In interviews he has claimed he was drugged, put on a plane, and then kept under 'psychological pressure' at an undisclosed location in the U.S.

There he was asked to hand over classified documents, but he claims he never did as he didn't want to betray his country.

He then walked into the Iranian interests section at the Pakistani Embassy in Washington and demanded to be sent home.

He came back to a hero's welcome and insisted he was a 'simple researcher'.

Amiri worked for a university affiliated with Tehran's extensive nuclear program.

He is said to have had an in-depth knowledge of Iran's nuclear program and was kept at a secret location after returning to the country.

According to CBS, he told officials in interviews he was being held against his will by Saudi and U.S. spies.

But American officials said he was set to receive millions for informing.

Amiri's mother told the BBC that his body had been sent to her with rope marks around his neck.

On Sunday, an Iranian judicial spokesman confirmed the execution had taken place.

He told the Mizan Online news site: 'Shahram Amiri was hanged for revealing the country's top secrets to the enemy (US).'

In another recording filmed when he was missing, the scientist suggested he had fled from the USA, where he had been held against his will.

But US officials said they paid Amiri some $5 million to defect and provide 'significant' information about Iran's atomic program.

Amiri later fled the U.S. without the money.

Iranian officials previously touted Amiri's claim he had been abducted by U.S. agents while on a pilgrimage to holy sites in Saudi Arabia.

They welcomed him home in 2010 as a hero.

But his family confirmed to the BBC he had been given a lengthy jail sentence after returning to the Middle East.

The State Department declined to comment on Amiri's execution.

Shakram Amiri appeared in a video in which he claimed to have been put under pressure to 'reveal sensitive information' by the CIA. Upon his return to Tehran, Iranian authorities backed up his claim and he came back to a hero's welcome

Amiri's disappearance will raise concerns about the future of Nazanin Zaghari-Ratcliffe, a British-Iranian aid worker being held by Tehran.

The 37-year-old, who was arrested as she tried to leave Iran after a visit with her two-year-old daughter, appeared in the Revolutionary Court on Monday.

'We continue to raise our strong concerns about British prisoners in Iran, including Mrs Zaghari-Ratcliffe, at the highest levels in both London and Tehran,' a spokeswoman for Britain's Foreign Office said.

Zaghari-Ratcliffe, 37, works for the Thomson Reuters Foundation, a London-based charity that is independent of Thomson Reuters and operates independently of Reuters News.

The Foreign Office spokeswoman said former Prime Minister David Cameron had repeatedly raised the case with his Iranian counterpart.

'We are deeply concerned by recent reports that Mrs Zaghari-Ratcliffe has been charged but has not been allowed to see a lawyer,' the spokeswoman said.

'We remain ready to facilitate Mrs Zaghari-Ratcliffe's daughter's return to the UK if requested.'