Iran confirmed on Friday that Foreign Minister Mohammad Javad Zarif had discussed prisoner releases with former US ambassador Bill Richardson, a day after the two countries each released one detainee.
A ministry official had said in December that Richardson, a former US envoy to the United Nations, had held talks with Zarif but played down their significance.
On Friday, ministry spokesman Abbas Mousavi said they had discussed the release of US navy veteran Michael White "months ago".
White, detained in Iran since 2018, was freed on Thursday in exchange for the United States allowing an Iranian-American physician to visit Iran, his lawyer and a US official said.
"Foreign Ministry spokesman Mousavi confirmed meeting of Bill Richardson with Zarif over the American detainee," state news agency IRNA said, referring to White. "We have always responded positively to humanitarian efforts that would lead to the release of Iranian hostages in the United States and elsewhere," it quoted Mousavi as saying.