Amir Mirzai Hekmati is seen speaking about his mission on Iranian state television in an unknown location in Iran, in this still frame taken from a video acquired December 18, (Photo: Reuters).
Iran opened a trial on Tuesday of an American of Iranian descent accused of spying for the US Central Intelligence Agency, the Fars news agency reported.
"The first hearing in the trial of Amir Mirzai Hekmati, recently arrested for spying for the United States, started Tuesday morning" in a Tehran court, Fars reported.
Hekmati, a 28-year-old former US Marine born in the US state of Arizona to an Iranian immigrant family, was shown on Iranian state television mid-December saying he was a CIA operative sent to infiltrate the Iranian intelligence ministry.
The US government says Hekmati has been falsely accused and has demanded his immediate release.
It also said that the Swiss embassy, which represents US interests in Iran, had not been given access to him.
Hekmati's trial opened against a backdrop of heightened tensions between arch foes Washington and Tehran.
The United States is leading a Western push to ratchet up sanctions on Iran over its controversial nuclear programme.
Each side has accused the other of conducting clandestine operations, with the United States alleging in October that Tehran had a hand in a thwarted plot to assassinate the Saudi ambassador to Washington, and Iran this month showing off a CIA drone it said it captured through cyber warfare.
Fars said the trial, taking place behind closed doors before a revolutionary court in the Iranian capital, started with the prosecutor saying Hekmati was charged with cooperating "with the hostile US government and the US espionage services of the CIA."
It said Hekmati had admitted to trying to infiltrate Iran's intelligence services for the CIA, and quoted what it said was a confession by the Iranian-American.
"I was fooled by the US intelligence services. Even though I entered Iran with the mission of infiltrating the Iranian intelligence services to become a source of information for the CIA, I did not want to personally hurt Iran because I had the intention of living in Iran and of not returning to the United States," Hekmati was quoted as saying, according to Fars.
The lawyer appointed to defend Hekmati criticised the accusation, Fars said, adding that the prosecutor rejected the lawyer's comments.
The judge handling the trial, Abolghasem Salavti, said he would deliver his verdict after hearing the defence lawyer's counter-argument.
US media quoted Hekmati's family as saying he had worked as an Arabic translator for the US Marines and had gone to Iran months ago to visit his Iranian grandmothers.
"My son is no spy," Hekmati's father, Ali Hekmati, a teacher in the US state of Michigan, told US television network ABC last week.