TEHERAN (AFP) - Iran has executed a nuclear scientist convicted of handing over "confidential and vital" information to the United States, a judicial spokesman said on Sunday (Aug 7).

"Shahram Amiri was hanged for revealing the country's top secrets to the enemy," Mr Gholamhossein Mohseni Ejeie told reporters in Teheran.

Amiri disappeared in Saudi Arabia in June 2009 and resurfaced a year later in the United States.

Conflicting accounts said he had either been abducted or had defected at a time when international tensions over Iran's nuclear programme were at their peak.

In a surprise move, Amiri then returned to Teheran in July 2010, saying he had been kidnapped at gunpoint by two Farsi-speaking CIA agents in the Saudi city of Medina.

At first he was greeted as a hero, telling reporters as he stepped off the plane at Teheran airport that he had resisted pressure from his US captors to pretend he was a defector.

He denied he was a nuclear scientist and said US officials wanted him to tell the media he had "defected on his own and was carrying important documents and a laptop which contained classified secrets of Iran's military nuclear programme".

"But with God's will, I resisted," Amiri said as he was welcomed home by his tearful wife and young son.

However, it was soon clear that Iranian authorities had not accepted this version of events and Amiri dropped out of public view. He was probably arrested although it was never officially reported.

Iran's judicial spokesman said on Sunday that the Iranian intelligence services had "outsmarted" the US.

"American intelligence services thought Iran has no knowledge of his transfer to Saudi Arabia and what he was doing but we knew all of it and were monitoring," Mr Ejeie told reporters.

"This person, having access to confidential and highly confidential information of the regime, had established a connection to our number one enemy, America, and had provided the enemy with Iran's confidential and vital information," he added.

Teheran and Washington have had no diplomatic ties since 1980, when students stormed the US embassy following the 1979 Islamic revolution.

"Shahram Amiri was tried in accordance with law and in the presence of his lawyer. He appealed his death sentence based on judicial process. The Supreme Court... confirmed it after meticulous reviews," he added.

Iran last year signed a landmark deal with world powers, including the US, to place curbs on its controversial nuclear programme in exchange for the lifting of economic sanctions.

Numerous media reports in recent years have supported the idea that Amiri was a defector with highly prized information on its nuclear programme.

"Shahram Amiri described to American intelligence officers details of how a university in Teheran became the covert headquarters for the country's nuclear efforts," the New York Times reported in July 2010, citing unnamed US officials.

"While still in Iran, he was also one of the sources for a much-disputed National Intelligence Estimate on Iran's suspected weapons program, published in 2007," the report said.

World powers had grown increasingly concerned that Iran was pursuing a nuclear weapon - a charge that it has consistently denied.

Between 2010 and 2012, four nuclear scientists were assassinated inside Iran and a fifth survived a bomb attack. The government blamed the attacks on US and Israeli intelligence services.

Iran finally reached a deal with world powers in July 2015, promising to curb its nuclear programme in exchange for a lifting of international sanctions.