Iran confirmed Tuesday ongoing "negotiations" with the United States over a potential prisoner swap, after a US official said Washington is working to release its detained citizens.

The US envoy for Iran, Robert Malley, said on Saturday that President Joe Biden insists on the release of all Americans and will not accept a "partial deal".

Malley called the release of Americans detained in the Islamic republic a "priority" and said that negotiations with Iran have "made some progress," NBC News reported.

Asked about Malley's remarks, Iran's government spokesman Ali Rabiei confirmed the talks and said Tehran calls for the release of all Iranian prisoners, not just those held in the US.

Iran "is ready to swap all political prisoners in exchange for freeing all Iranian prisoners across the world," he told reporters at a televised press conference.

They include those "who have been detained upon US orders" or at Washington's request, he added, saying that "the negotiations on this issue are ongoing".

Iran's foreign ministry spokesman Saeed Khatibzadeh said Monday that Foreign Minister Mohammad Javad Zarif had "put forth a plan to swap all Iranian and American prisoners", state news agency IRNA reported. 

"Biden's administration also considered this issue from the first day" in office, he added.

The remarks came as Iran has engaged in talks with world powers in Vienna on reviving its 2015 nuclear deal.

The agreement, which limited Iran's nuclear programme in exchange for international sanctions relief, has been on life support since former US president Donald Trump withdrew from it in 2018 and reimposed sanctions.

Arrests of foreigners in Iran -- especially dual nationals who are often accused of espionage -- have increased since then.

Tehran and Washington have held indirect negotiations in the Austrian capital since early April.

The two countries in May denied having concluded a prisoner exchange deal, following reports that an agreement was made on the sidelines of the Vienna talks to release four prisoners from each side.

Iran and the US have had no diplomatic relations since 1980, and tensions between them worsened during Trump's tenure.

But they 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.

The most prominent exchange between them came in 2016, months after the nuclear deal was clinched, with four Americans released in exchange for seven Iranians.