The US has asked Iran to free "without delay" a US man of Iranian descent described by Tehran as a CIA spy, BBC reported.
Amir Mirzai Hekmati confessed he had been sent to infiltrate Iranian intelligence services on state TV.
A spokeswoman for the State Department told the BBC the U.S. had requested access to Mr Hekmati through the embassy of Switzerland, which serves as an intermediary between the countries.
His family denied their son was involved in espionage.
"My son is no spy. He is innocent. He's a good fellow, a good citizen, a good man," Ali Hekmat told ABC News. "These are all unfounded allegations and a bunch of lies."
A state department spokeswoman told the BBC: "The Iranian regime has a history of falsely accusing people of being spies, of eliciting forced confessions, and of holding innocent foreigners for political reasons."
On Sunday, the Iranian TV report said Mr Hekmati had come to the attention of Iranian agents at Bagram air base in Afghanistan, before he went to Iran.
He was shown speaking Farsi and English, describing his alleged mission to infiltrate Iran's intelligence ministry. The report said Mr Hekmati joined the US Army in 2001 and received special training before being sent to Iran.
According to the Ali Hekmati, his son did join the US military in 2001, but served in the Marines, where he was an Arabic translator. Iran's government has repeatedly accused the United States of carrying out covert intelligence operations in order to undermine it.
In May, Tehran claimed it had detained a network of 30 CIA operatives, saying they had been involved in espionage and sabotage. Last week, Iran indicted 15 people on charges of spying for America and Israel but gave few other details.