An Iranian court has convicted an American man of working for the CIA and sentenced him to death, state radio reported on Monday, in a case adding to the accelerating tension between the United States and Iran.

Iran charges that as a former U.S. Marine, Amir Mirzaei Hekmati received special training and served at U.S. military bases in Iraq and Afghanistan before heading to Iran for his alleged intelligence mission. The radio report did not say when the verdict was issued. Under Iranian law, he has 20 days to appeal.

The 28-year-old former military translator was born in Arizona and graduated from a high school in Michigan. His family is of Iranian origin. His father, a professor at a community college in Flint, Michigan, has said his son is not a CIA spy and was visiting his grandmothers in Iran when he was arrested.

The court convicted him of working with a hostile country, belonging to the CIA and trying to accuse Iran of involvement in terrorism, Monday’s report said. U.S. State Department has demanded Mr. Hekmati’s release

In its ruling, a branch of Tehran Revolutionary Court described Mr. Hekmati as a mohareb, an Islamic term that means a fighter against God, and a mofsed, or one who spreads corruption on earth. Both terms appear frequently in Iranian court rulings.

In a closed court hearing in late December, the prosecution asked for the death sentence for Mr. Hekmati.

The U.S. government has called on Iranian authorities to grant Swiss diplomats access to Mr. Hekmati in prison. The Swiss government represents U.S. interests in Iran because the two countries don’t have diplomatic relations.

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