Amir Mirza Hekmati, a 28-year-old of Iranian descent, could face the death penalty if found guilty of cooperating with a hostile government and spying for the CIA. He was arrested in December.
Iran's Intelligence Ministry accused Hekmati of receiving training at US bases in neighbouring Afghanistan and Iraq.
Shortly after his detention, state television showed a taped interview of him confessing to being a spy. At his trial he admitted to having links with the CIA but said he had no intention of harming Iran.
The trial comes at a time of heightened tension between Iran and the US, which is leading efforts to tighten sanctions on Tehran because of its controversial nuclear programme.
US State Department spokesman Mark Toner last week urged Tehran to release Hekmati immediately. He said that Switzerland, which represents US interests in Iran in the absence of formal diplomatic ties, had formally requested permission for consular access to Hekmati on December 24 but Iran had refused.
"America's request for the return of the accused, indicates their utmost impudence and he should be tried based on the country's laws," justice ministry spokesman Gholamhossein Mohseni-Ejei said.
Iran said in May it had arrested 30 people on suspicion of spying for the United States, and 15 people were later indicted for spying for Washington and Israel.
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