Iranian officials have long maintained that Amiri was kidnapped by the CIA while he was performing pilgrimmage in Mecca last year.
On June 29, Iranian television screened a video of a man claiming to be Amiri and saying that he had managed to escape from the hands of US intelligence agents in Virginia.
"I could be rearrested at any time by US agents ... I am not free and I am not allowed to contact my family. If something happens and I do not return home alive, the US government will be responsible," he said.
"I ask Iranian officials and organisations that defend human rights to raise pressure on the US government for my release and return to my country," the man said, adding he has not "betrayed" Iran.
A US official on Tuesday dismissed the allegations in the Iranian broadcast.
Before that video, two others said to show Amiri appeared on the internet.
In the first, broadcast on Iranian TV, a man says he was abducted and was being held in the United States.
He said he was forced to take part in a media interview "to claim that I was an important figure in Iran's nuclear programme and that I had sought asylum in America of my own free will".
But in a second video, a man also purporting to be Amiri says he was actually studying in the United States.
US-based ABC news reported in March that Amiri had defected and was working with the CIA.
US officials have rejected these allegations, but Iran claims it has numerous citizens in secret detention in the US, including a former deputy defence minister who disappeared in 2007.
Iranian media often link the case of three US citizens, arrested near the Iraqi border a year ago where they say they were hiking and held on suspicion of spying, to the fate of alleged Iranian detainees in the United States.
Some Iranian politicians have called on the United States to propose a prisoner swap.