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An Iranian nuclear scientist caught up in a real-life U.S. spy mystery who later returned to his homeland and disappeared has reportedly been executed under similarly mysterious circumstances.

Foreign media reports say Shahram Amiri was hanged this week and a memorial service for him was held in Kermanshah, 500 kilometers (310 miles) southwest of Tehran. The reports cited his mother, whom The Associated Press was unable to reach.

State media in Iran, which has been silent about Amiri's case for years, has not reported his death. Officials in Iran's judiciary could not be reached for comment. Iran's mission to the United Nations did not immediately respond to a request for comment Sunday.

Amiri disappeared in Saudi Arabia in 2009, reappearing a year later in the U.S. He later returned home.