An American man in Iran has been sentenced to death after a court convicted him of spying for the CIA, state radio reported Monday.

Iran maintains that Amir Mirzaei Hekmati, a former U.S. Marine, underwent special training before heading to the Middle Eastern state on an alleged intelligence mission.

Under Iranian law, the 28-year-old has close to three weeks to appeal the sentence.

"He has 20 days to appeal but this is a pretty dramatic situation and the Americans are quite worried," said CTV's London Bureau Chief Tom Kennedy.

The court convicted Hekmati of working with a hostile country, belonging to the CIA and attempting to accuse Iran of terrorism, a Monday report said.

His death sentence comes against the backdrop of deteriorating ties between Iran and the United States.

As the two nations clash over Iran's nuclear program, which Washington has long been suspicious of, Kennedy said the U.S. is worried that existing animosity will carry over into Hekmati's case.

"What worries them is it could be a factor in whatever Mr. Hekmati's fate is going to be," he told Â鶹´«Ã½ Channel on Monday.

Meanwhile, the U.S. State Department has demanded Hekmati's release.

It's unclear when the former military translator was arrested, but some reports have pegged the date as late August or early September.

Access to information, said Kennedy, has been a problem throughout Hekmati's detainment.

"There was no consular access given to Mr. Hekmati during this process," he said. "It's one of the Americans' premier complaints."

While the U.S. doesn't have diplomatic ties to Iran, the country has asked Iran to allow Swiss diplomats access to Hekmati.

"As to what specific evidence the Iranians had, we don't know," said Kennedy.

In a December interview, Hekmati's father told the Associated Press that his son went to Iran about four months earlier to visit his grandmothers.

That same month, Iranian state television broadcast footage of Hekmati reciting an alleged confession in which he admitted to trying to infiltrate Iran's Intelligence Ministry.

Hekmati is a dual U.S.-Iranian national who was born in Arizona and graduated from high school in Michigan. His family has fervently denied Iran's accusations.

With files from The Associated Press