It has been reported that five US-Iranian dual nationals have been released and placed under house arrest in Iran.

An attorney for one of the men said Siamak Namazi, Emad Shargi, and Morad Tahbaz, who also has a British passport, were released alongside a fourth unidentified man.

An official from the US national security agency said that a fifth American had already been released.

It had been agreed that their release would be negotiated between Iran and the US.

Adrienne Watson, spokesperson for the National Security Council, said, “While this is an encouraging move, these US citizens should not have been detained in the first place.”

“We will not rest until they all return home to the United States,” she said.

State media reported that Iran’s UN mission confirmed the release of dual nationals from Tehran’s Evin prison.

In accordance with the deal, frozen funds in South Korea would be “unblocked and transferred to Qatar,” according to Reuters, citing state news agency IRNA.

Several US media outlets report that Iranian funds frozen in South Korea are worth around $6 billion (£4.7 billion).

Babak Namazi, Mr Namazi’s brother, said: “This is a positive change, but we won’t rest until Siamak and others return home.”

After being arrested in 2015, the 51-year-old was sentenced to 10 years in prison.

After Shargi’s detention in April 2018, his sister said she “has faith in the efforts of President Biden and government officials” to secure his release.

The arrest of Mr Tahbaz, a 67-year-old businessman and wildlife conservationist, occurred in January 2018.

A number of dual nationals have been detained and imprisoned in Iran in recent years, usually on national security charges.

Several of the five people released wish to remain anonymous, according to State Department spokesman Matthew Miller.

Continuing, he said: “We are in close contact with the families of US citizens involved, and we continue to monitor their health and welfare closely.”

A prisoner swap with Iranians now incarcerated in American prisons and other western prisons, along with the easing of US sanctions on Iran, has been discussed for years to try to secure their release.

A Reuters report said the US citizens may still have to wait several weeks to depart Iran, citing sources close to the talks.

According to the New York Times, Iranian prisoners in US jails may also be released as part of the deal, but the White House has not confirmed what it offered to Tehran to secure their release.