The United States on Monday confirmed a prisoner swap with Iran and said that President Joe Biden had granted clemency to five Iranians jailed or awaiting trial for non-violent crimes.

A US official said that seven US citizens were on a Qatari plane that departed Iran. They include three previously identified Americans – Siamak Namazi, Morad Tahbaz and Emad Sharqi – and two who wish to remain anonymous.

Also on the plane are Namazi's mother and Sharqi's wife, both of whom are US citizens who were barred from leaving Iran, although they were not imprisoned.

All are of Iranian descent and are considered citizens by Tehran, which does not recognise dual nationality.

The US official said that Biden, in taking the politically risky move, was also imposing new sanctions on Iran's intelligence ministry and former president Mahmoud Ahmadinejad.

The sanctions were imposed over alleged deceit over the disappearance of Bob Levinson, a former FBI agent who disappeared in Iran in mysterious circumstance and is presumed dead.

"The United States will never give up on Bob Levinson's case. We call on the Iranian regime to give a full account of what happened to Bob Levinson," a senior US official said on condition of anonymity.

Levinson had travelled to the Iranian island of Kish on a CIA mission. Iran has not acknowledged his arrest.

The US official said that the five Iranians granted clemency were all charged or convicted with nonviolent crimes." Two were in prison, with the sentence of one soon to end, and three were awaiting trial. (AFP)