Tehran, Iran (CNN) -- Iran has sentenced a former U.S. Marine to death, accusing him of espionage. A court convicted Amir Mirzaei Hekmati of "working for an enemy country," as well as membership in the CIA and "efforts to accuse Iran of involvement in terrorism," the semi-official Fars news agency reported Monday. Hekmati's family and the U.S. government deny the allegations. The sentence came down five months after Hekmati's arrest. The news came amid rising tensions between the United States and Iran. The International Atomic Energy Agency confirmed Monday that uranium enrichment has begun at a nuclear facility in northern Iran. Iranian President Mahmoud Ahmadinejad was on a visit to Venezuela, where President Hugo Chavez said the two of them were working together to stop the "imperial insanity" of the United States.
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White House: The U.S. takes the matter "very seriously"
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An Iranian court finds Amir Hekmati "corrupt on Earth," state media say
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He was arrested in August while visiting relatives
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Prosecutors allege he was hired to deliver information to Iran
Three @placeholder hikers, also accused of spying, were arrested in 2009 and ultimately released.