"I totally trusted the Islamic Republic and the Republic was confident that I was not defecting to the US," he said during the interview.
Amiri, who claims he was abducted in Saudi Arabia by the CIA 14 months ago, returned to Tehran, the capital of Iran, on Wednesday.
But US officials deny kidnapping Amiri and insist he was living freely in the United States.
US officials have countered his claims aggressively, calling Amiri's story a "fairy tale".
Amiri is at the centre of a volatile war of words between Iran and the US, with each country trading public salvos designed to discredit the other.
The Washington Post reported on its website late on Friday that Amiri had for some time been providing the CIA with information about Iran's nuclear programme while he was still in Iran.
The report said he was one of two informants the agency whisked out of the country last year because of concerns that the Tehran government had discovered they were providing secrets.
For the moment, the Iranian scientist is a national hero, but after his public role is done, former CIA officials say, he will likely face intense questioning about his defection from Iran's ministry of intelligence and security.