Iran has executed an Iranian nuclear scientist detained in 2010 when he returned home from the US,after a court convicted him of spying for Washington. 

Shahram Amiri was given a hero's welcome in 2010 when he returned to Tehran -- after disappearing during a Saudi pilgrimage in 2009 before resurfacing in the United States.

But he was soon arrested in Iran and tried for treason -- reportedly for giving "vital information" about the country to the US through his American connections.

Now, Iran's judiciary says the nuclear scientist has been executed for treason -- after Iran's Supreme Court upheld his conviction of spying for Washington.

A US official had said 2010 that the U.S. had indeed received "useful information" from him.

Amiri was a university researcher working for Iran's Atomic Energy Organization.

Iran had accused the CIA of kidnapping him.

But US officials had said Amiri was free to come and go as he pleased and that he may have returned to Iran because of pressures on his family back home.

Although in a 2010 video on state TV, Amiri himself said he had fled from US agents.

Relations between Iran and the US have been thawing after last year's landmark nuclear deal.

It curbs Tehran's nuclear ambitions in exchange for a lifting of economic sanctions.