Five US citizens left Iran and landed in Doha on Monday in a prisoner swap for five Iranians held in the United States and the transfer of $6 billion in Iranian funds, marking a rare moment of cooperation between the long-time antagonists.

"Today, five innocent Americans who were imprisoned in Iran are finally coming home," US President Joe Biden said in a statement shortly before the US detainees descended the stairs of a Qatari jet to be embraced by US diplomats.

A US-bound aircraft later departed the Qatari capital with the five Americans on board, sources with knowledge of the situation said.

Separately, Iran's Press TV said the five Iranians held by the United States and charged with committing crimes had been freed, an apparent reference to their being granted clemency. Two arrived in Doha, US and Iranian officials said.

"This was purely a humanitarian action," Iranian President Ebrahim Raisi said after arriving in New York for the annual UN General Assembly. "It can certainly be a step based upon which in the future other humanitarian actions can be taken."

It was unclear whether the exchange might bring progress on the many issues that divide the two nations, including Iran's nuclear program, its support for regional Shi'ite militias, the presence of US troops in the Gulf and US sanctions on Iran.

Relations between the United States and Iran, adversaries for more than 40 years, have been especially bitter since former US President Donald Trump in 2018 reneged on a deal to curb Iran's nuclear program and reimposed US sanctions.

Washington suspects the program may aim to develop nuclear weapons - an ambition Tehran denies - that could threaten Israel or US Gulf Arab allies.

US Secretary of State Antony Blinken left the door open to diplomacy on the nuclear file, which he described as "perhaps the number one issue of concern", but suggested nothing was imminent.

"In this moment, we're not engaged on that, but we'll see in the future if there are opportunities," he told reporters in New York.

US analysts voiced skepticism that progress was likely soon on the nuclear or other issues.

"The prisoner swap does likely pave the way for additional diplomacy around the nuclear program this fall, although the prospect for actually reaching a deal is very remote," said Henry Rome of the Washington Institute for Near East Policy.

"Removing an irritant is different from adding a salve," said Jon Alterman of the Center of Strategic and International Studies.

Tough on Iran

In a sign Biden, a Democrat, wishes to appear tough on Iran and perhaps blunt Republican criticism, he announced fresh US sanctions on Iran's former president Mahmoud Ahmadinejad and its intelligence ministry for "involvement in wrongful detentions".

"We will continue to impose costs on Iran for their provocative actions in the region," he said in the statement, in which he thanked the governments of Qatar, Oman, Switzerland and South Korea for their assistance in securing the releases.

Qatar mediated indirect US-Iran talks on the prisoners while Switzerland, which represents US interests in Tehran because the United States and Iran do not diplomatic relations, helped with the transfer of funds from South Korea to Qatar.

A plane sent Qatar flew the five US citizens and two of their relatives out of Tehran after both sides got confirmation the $6 billion was transferred from South Korea to Qatari accounts, a source briefed on the matter told Reuters.

A prominent Republican, House Foreign Affairs Committee Chairman Michael McCaul, said the transfer of the $6 billion would likely lead to more detentions of US citizens by Iran.

"I am very concerned that this $6 billion hostage deal incentivises future hostage-taking," McCaul said in an emailed statement. "There is no question this deal will free up funds for Iran's malign activities."

Biden aides argue the money belongs to Iran and is being transferred from restricted South Korean accounts to restricted Qatari accounts, where it can only be spent on food, medicine and other humanitarian items with US oversight.

Earlier, two of the five Iranians landed in Qatar, a US official said. Three have opted not to return to Iran.

The five Iranian Americans - one of whom had been held for about eight years on charges the United States had rejected as baseless - were due to board a US government aircraft in Doha and then fly home to the United States.

The deal, after months of talks in Qatar, removes a major irritant between the US, which brands Tehran a sponsor of terrorism, and Iran, which calls Washington the "Great Satan".

The US dual citizens released include Siamak Namazi, 51, and Emad Sharqi, 59, both businessmen, and Morad Tahbaz, 67, an environmentalist who also holds British nationality.

The identities of the fourth and fifth US citizens were not disclosed at their request given their desire for privacy.

Iranian officials have named the five Iranians released by the US as Mehrdad Moin-Ansari, Kambiz Attar-Kashani, Reza Sarhangpour-Kafrani, Amin Hassanzadeh and Kaveh Afrasiabi.

(FRANCE 24 with Reuters)

Originally published on France24