The US government and Iran have reached an agreement to release five dual US-Iranian nationals in exchange for the release of $6bn in seized Iranian oil funds.

As part of the agreement between Tehran and Washington, which has taken more than two years of back-channel talks via regional intermediaries, five US nationals have been released from prison in Iran and have been transferred to “house arrest”, according to officials at the State Department, sources in the US told the New York Times.

“We have received confirmation that Iran has released from prison five Americans who were unjustly detained,” Adrienne Watson, the National Security Council spokeswoman, said in the newspaper.

She added that US citizens “should have never been detained in the first place. We will continue to monitor their condition as closely as possible.” Watson added, “Negotiations for their eventual release remain ongoing and are delicate.”

Iran’s mission to the United Nations told Iranian media that the two countries have agreed to “reciprocally release and pardon five prisoners”.

“This release was made within the framework of an agreement with the mediation of a third country so that the parties reciprocally release the five prisoners in question and make them subject to amnesty.”

A source in Tehran later confirmed that as soon as the funds seized by the US are transferred to the Qatari Central Bank account from South Korea, where money has been trapped under Treasury Department orders, Iranian prisoners will be fully released, and unnamed Iranian prisoners will also be released.

“It's worth noting that this agreement was supposed to be finalised last year, but the subsequent unrest and misconceptions caused the Americans to hesitate”, the source added.

The three known dual nationals, Siamak Namazi, Emad Sharghi, and Morad Tahbaz, who were imprisoned on unproven espionage charges, and two other Americans whose identities are kept confidential, have been released.

Sources familiar with the release details revealed that one of the undisclosed Americans is a scientist, while the other is a businessman.

Another detainee, an American woman, was previously placed under house arrest, as per multiple sources who requested anonymity while discussing the finalised agreement.