"The reports from informed sources are not confirmed, as it was said in the past," foreign ministry spokesman Saeed Khatibzadeh told a news conference.

But he added that "there are always plans and ideas to be pursued", without elaborating.

His comments came after outlets including Iranian state television on Sunday quoted an "informed" source saying that Tehran and Washington would swap prisoners.

"Under pressure from the (US) Congress and the need for immediate results" in the nuclear file, "the Americans agreed to pay $7 million and release four Iranians... in exchange for four American spies," the source reportedly said.

A senior White House official had also denied the report on Sunday.

"There is no agreement to release these four Americans," White House chief of staff Ron Klain said on CBS's "Face the Nation".

"We're working very hard to get them released. So far there is no agreement to bring these four Americans home," he said.

Iran's state broadcaster also reported that British-Iranian dual national Nazanin Zaghari-Radcliffe, who has been held in the country since 2016, would be freed -- but British officials played down that report.

The reports came as Iran takes part in talks with world powers over reviving the 2015 deal over its nuclear programme.

On Saturday, negotiators meeting in the Austrian capital Vienna expressed "cautious and growing optimism" for a solution.

The agreement, which curbs Iran's nuclear program in exchange for sanctions relief, has been on life support since then-US president Donald Trump withdrew in 2018.

Khatibzadeh said Monday that the issue of prisoners "has and always will be a humanitarian one, and figures on Iran's agenda, regardless of any negotiations".

Iran and the United States have had no diplomatic relations since 1980, and tensions between the two countries worsened during Trump's tenure.

But the two countries have released each others' citizens in the past, most recently in June 2020, when the US freed Iranian scientist Majid Teheri as Tehran set free US Navy veteran Michael White.

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CBS CORPORATION