Five Americans freed from Iran have made an emotional return to the United States a day after they were swapped for five Iranians held in the US and the unfreezing of Iranian funds.

Coming off the plane, the returning Americans were embraced by family and friends with smiles, laughs, and visible emotion, video footage from the airport showed.

One of the returnees briefly waved a small US flag handed to him.

“The nightmare is finally over,” said Babak Namazi, speaking with his arm around his returning brother Siamak at Fort Belvoir, Virginia, on Tuesday.

The welcome ceremony followed a carefully choreographed exchange, agreed after months of Qatar-mediated talks, that was triggered on Monday when the $US6 billion ($A9.3 billion) in funds that had been blocked in South Korea were wired, via Switzerland, to banks in Doha.

After the transfer was confirmed, the five US prisoners plus two relatives took off on a Qatari plane from Tehran, at the same time as two of the five Iranian detainees landed in Doha on their way home. Three Iranians chose not to go to Iran.

The deal removes a point of friction between the United States, which brands Tehran a sponsor of terrorism, and Iran, which calls Washington the “Great Satan”.

The freed Americans include US-Iranian dual citizens Siamak Namazi, 51, and Emad Sharqi, 59, both businessmen, and Morad Tahbaz, 67, an environmentalist who also holds British nationality. Two of them have not been publicly identified.

US President Joe Biden welcomed the return of the prisoners home in a statement on Monday but his administration also announced fresh US sanctions.

“We will continue to impose costs on Iran for their provocative actions in the region,” he said.

Iranian President Ebrahim Raisi, who was in New York for the annual UN General Assembly, called the swap a humanitarian action.

“It can certainly be a step based upon which in the future other humanitarian actions can be taken,” he added.

Biden, a Democrat, has faced criticism from Republicans over the deal. House Foreign Affairs Committee Chairman Michael McCaul, a prominent Republican, said the transfer of the funds could encourage Iran to detain more US citizens.

Biden aides say the money belongs to Iran and is being transferred from restricted South Korean accounts to restricted accounts in Qatar, which will monitor the cash to ensure it is spent on humanitarian goods not items under US sanctions.

Relations between the United States and Iran have been especially bitter since 2018 when then-president Donald Trump pulled out of a deal aimed at curbing Tehran’s nuclear ambitions and toughened US sanctions.

Washington suspects Iran’s nuclear program may be aimed at developing nuclear arms, a charge Iran denies.

US Secretary of State Antony Blinken left the door open to nuclear diplomacy, but suggested nothing was imminent.

-Reuters