The White House has defended a $US6 billion ($9.3 billion) prisoner swap with sworn enemy Iran as five US citizens who were detained for years had their first taste of freedom.

The five Americans left Iran and landed in Doha, Qatar, on Tuesday morning (AEST) in a prisoner swap for five Iranians held in the US.

The deal involved the transfer of billions of dollars in Iranian funds in a rare moment of co-operation 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.

Separately, Iran’s Press TV said the five Iranians detained by US 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.

Republicans have criticised Biden for paying what they say amounts to ransom for the US detainees.

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

It was unclear whether the exchange might bring progress on the many issues that divide the two governments, 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.

In a sign Biden, a Democrat, wishes to keep a tough front toward Iran and perhaps blunt Republican criticism, he announced US sanctions on Iran’s former Iranian president Mahmoud Ahmadinejad and its intelligence ministry “for their 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.

A plane sent by mediator Qatar flew the five US citizens and two of their relatives out of Tehran after both sides got confirmation $US6 billion ($9.3 billion) was transferred from South Korea to Qatari accounts, a source briefed on the matter told Reuters.

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

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

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

A senior US administration official said the deal did not change its adversarial relationship with Iran, but the door was open for diplomacy on Iran’s nuclear program.

“If we see an opportunity, we will explore it but right now, I’ve really nothing to talk about,” the official said, speaking on condition of anonymity.

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.

Iranian media identified the two men who landed at Doha as Moin-Ansari and Sarhangpour-Kafrani.

Two Iranian officials previously said that Afrasiabi would remain in the US but had not mentioned others.