A man who says he is an Iranian nuclear scientist claims to have escaped after being abducted by US agents.
In a video shown on Iranian state TV, he says he has escaped in the US state of Virginia and is now on the run.
Mr Amiri disappeared a year ago while undertaking the Hajj in Saudi Arabia.
Two videos purportedly showing him surfaced three weeks ago. One said he had been kidnapped, the other that he was living freely in Arizona.
The US has strenuously denied abducting him, but ABC News reported in March that Mr Amiri had defected and was helping the CIA compile intelligence on Iran's controversial nuclear weapons programme.
The state department has refused to say whether he is in the US.
In the new video, broadcast on Tuesday, a man claiming to be the missing scientist says: "I, Shahram Amiri, am a national of the Islamic Republic of Iran and a few minutes ago I succeeded in escaping US security agents in Virginia.
"Presently, I am producing this video in a safe place. I could be re-arrested at any time."
The man says the video broadcast earlier this month - in which someone claiming to be Mr Amiri says he was kidnapped by Saudi and US agents, tortured, forced to say he had defected and was living in Tucson, Arizona - is "completely authentic and there are no fabrications in it.
"The second video which was published on YouTube by the US government, where I have said that I am free and want to continue my education here, is not true and is a complete fabrication.
"I am not free here and I am not permitted to contact my family. If something happens and I do not return home alive, the US government will be responsible."
He finishes the video by urging Iranian officials and human rights organisations to "put pressure on the US government for my release and return".
"I was not prepared to betray my country under any kind of threats or bribery by the US government," he adds.
A US official told the AFP news agency the allegations were "ludicrous".
Iranian media have said Mr Amiri worked as a researcher at a university in Tehran, but some reports say he worked for the country's atomic energy organisation and had in-depth knowledge of its nuclear programme.