An image shared by Labour MP Tulip Siddiq on Twitter of Nazanin Zaghari-Ratcliffe on a plane, heading for the UK. /Twitter/@TulipSiddiq

Britain confirmed the release by Iran of British-Iranian dual nationals Nazanin Zaghari-Ratcliffe and Anousheh Ashouri, saying they would return to Britain later on Wednesday.

"I am very pleased to confirm that the unfair detention of Nazanin Zaghari-Ratcliffe and Anousheh Ashoori in Iran has ended today, and they will now return to the UK," Prime Minister Boris Johnson said on Twitter.

A third dual-national Morad Tahbaz was released from prison in Iran on furlough, foreign minister Liz Truss said on Twitter.

"We will continue to work to secure Morad's departure from Iran," Truss added.

A British lawmaker in contact with Zaghari-Ratcliffe and her family tweeted a picture of her smiling and said it showed her on board a plane.

"Nazanin is now in the air flying away from 6 years of hell in Iran," the lawmaker, Tulip Siddiq tweeted.

Six years detained

Zaghari-Ratcliffe, a project manager with the Thomson Reuters Foundation, was arrested at a Tehran airport in April 2016 and later convicted by an Iranian court of plotting to overthrow the clerical establishment.

Her family and the foundation, a charity that operates independently of Thomson Reuters and its news subsidiary Reuters, deny the charge.

Ashouri was sentenced to 10 years in jail in 2019 for spying for Israel's Mossad and two years for "acquiring illegitimate wealth," according to Iran's judiciary.

Debt paid

Zaghari-Ratcliffe release was also announced by the Iranian Fars news agency, which stated she was handed over to a British team at the International Imam Khomeini Airport. 

"Britain released $530 million...ahead of the release," Fars said, in reference to the UK's long-standing 400-million-pound ($520 mln) debt.

Iran's clerical rulers say Britain owes the money that Iran's Shah paid upfront for 1,750 Chieftain tanks and other vehicles, almost none of which were delivered after the Islamic Revolution of 1979 toppled the U.S.-backed leader.