An Iranian court has convicted a US man of working for the CIA and sentenced him to death, according to a state radio report, amid tensions between Iran and the international community over a suspected new nuclear facility.
Iran says that Amir Mirzaei Hekmati received special training and served at US military bases in Iraq and Afghanistan before heading to Iran for his alleged intelligence mission.
The radio report on Monday did not say when the verdict was issued. Under Iranian law, he has 20 days to appeal.
The Obama administration denied that Hekmati was a CIA spy, and sharply criticised the Islamic Republic for what it called a pattern of arresting innocent people for political reasons.
The 28-year-old former military translator being held in Iran was born in Arizona and graduated from 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.
Hekmati's trial took place as the US announced new, tougher sanctions against Iran over its nuclear programme.
The US and other Western countries believe Iran is developing atomic weapons, an accusation Iran denies.
The Iranian court's decision came on a day the US gave warning that if Iran was enriching uranium to 20 per cent at an underground facility at Fordow, this would be a "further escalation" of its pattern of violating obligations under UN Security Council resolutions.
The International Atomic Energy Agency (IAEA), the UN nuclear watchdog, confirmed on Monday that Iran had started enriching uranium up to 20 per cent at the site at Fordow, near the city of Qom, and that all atomic material there was under its surveillance.
"The fact that the IAEA has made clear that they are enriching to a level that is inappropriate at Fordow is obviously a problem," Victoria Nuland, the state department spokesperson, said at her daily briefing.
She said the IAEA's assessment, previously reported by diplomats in Vienna, did not come as a surprise to the US.
"If they are enriching at Fordow to 20 per cent, this is a further escalation of their ongoing violations with regard to their nuclear obligations," Nuland said, referring to a series of Security Council resolutions calling on Iran to halt its enrichment-related activities.
The state department also demanded Hekmati's release.
The Iranian court convicted Hekmati of working with a hostile country, belonging to the CIA and trying to accuse Iran of involvement in terrorism, Monday's report said.
In its ruling, a branch of the Tehran Revolutionary Court described 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 penalty for Hekmati.
PJ Crowley, former US state department spokesman, told Al Jazeera that an actual execution of Hekmati "would be very tragic and would really close the door on any normalised relations between the US and Iran".
"The crack is not wide as it is," he said. "We can never predict that it cannot get worse but it obviously can."
The US government has called on Iranian authorities to grant Swiss diplomats access to him in prison. The Swiss government represents US interests in Iran because the two countries don't have diplomatic relations.
Hekmati is a dual US-Iranian national, but Iran considers him merely Iranian since the country's law does not recognise dual citizenship.
The Marine Corps said "Amir Nema Hekmati" served between 2001 and 2005, including one deployment to Iraq in 2004 and a stint at the military language institute in Monterey, California.
The Marine records do not indicate any deployment to Afghanistan. It was not clear why the middle name was listed differently.
Similar cases against Americans accused of spying have heightened tensions throughout the confrontation over Iran's nuclear programme.
On December 18, Iran's state TV broadcast video of Hekmati delivering a purported confession.
In a statement released the same day, Iran's intelligence ministry said its agents had identified Hekmati at Bagram Air Field in neighbouring Afghanistan. Bagram is the main base for American and other international forces outside Kabul, the Afghan capital.
It is not clear exactly when he was arrested, although Iranian news reports have said he was detained in late August or early September.
At the time of his trip to Iran, Hekmati had been working in Qatar as a contractor for a company "that served the marines", his father said, without providing specific details.