Frozen funds totaling $6 billion have been transferred to Qatari banks under a United States-Iran prisoner swap deal, with a plane on standby in Tehran to fly out five American detainees, a source told Agence FrancePresse (AFP) on Monday.

The release of the funds by US ally South Korea, long blocked under US sanctions, is the key condition for the exchange of five Americans detained in Iran and, according to Tehran, five Iranians held in the US.

Qatar, which acted as the mediator, as Washington and Tehran do not have diplomatic relations, has informed both sides of the transfer, said the source briefed on details of the matter.

“Iranian and US officials have been notified by Qatar that all $6 billion has been transferred from Switzerland to bank accounts in Qatar,” added the source, who requested anonymity.

“A Qatari jet is on standby in Iran to bring the five US citizens and two relatives to Doha,” the source said.

Iran earlier voiced hope that the prisoner swap with the US would happen on Monday.

“We hope to have total access to the Iranian assets today,” Iran’s Foreign Ministry spokesman Nasser Kanani told a news conference in the capital Tehran. “The prisoner exchange will take place on the same day and five Iranian citizens imprisoned in America will be released.”

Iran had generated the $6 billion through oil sales to South Korea, which froze the funds after the US under former president Donald Trump reimposed sanctions as he withdrew from a landmark nuclear accord.

The five Americans — all considered Iranian citizens by Tehran, which rejects dual nationality — were released to house arrest when the deal was agreed last month.

Among the Americans is Siamak Namazi, a businessman arrested in 2015 on spying charges, which his family has rejected.

The others are wildlife conservationist Morad Tahbaz, venture capitalist Emad Sharqi and two others who wished to remain anonymous.

Last week, the official Islamic Republic news agency identified the five Iranian prisoners.

They include Reza Sarhangpour and Kambiz Attar Kashani, both accused of having violated US sanctions against Tehran.

A third prisoner, Kaveh Lotfolah Afrasiabi, was detained at his home near Boston, Massachusetts in 2021 and charged with being an Iranian government agent, US officials said.

The remaining two, Mehrdad Moein Ansari and Amin Hasanzadeh, were said to have links to Iranian security forces.

Out of the five Iranians to be released, two will return to Iran while two others will remain in US upon their request, said Kanani. The fifth will travel to a third country, he added.

The White House has denied that the unfreezing of the Iranian funds was effectively a ransom payment.

US President Joe Biden’s administration has insisted that Iran will only be allowed to use the money to buy food, medicine and other humanitarian goods.

Iran, which has been deeply hostile to the US since the country’s 1979 Islamic Revolution overthrew its proWestern monarch Mohammad Reza Pahlavi, has denied restrictions have been placed on the spending of funds.

Kanani has insisted that the money will allow Tehran to “purchase all nonsanctioned goods,” not just food and medicine.

Biden took office with hopes of restoring the landmark 2015 nuclear agreement, under which Iran promised to constrain its contested nuclear work in return for sanctions relief.

But months of talks failed to produce a breakthrough.

Prospects for resolving the dispute sank further after protests broke out in Iran a year ago following the death in policy custody of Mahsa Amini, who had been arrested for allegedly violating the country’s Islamic dress code.

The release of the funds and the prisoners came days after the first anniversary of her death, and as Biden and Iranian President Ebrahim Raisi are in New York City for the annual United Nations General Assembly, although they are not expected to meet.