An Iranian-American environmentalist who has been imprisoned by Iran has now been moved to a residential location, Britain's Foreign Office said on Monday.

Morad Tahbaz, who also holds British citizenship and whose family say he was born in Britain, had been taken back to prison on Friday after being released on furlough on Wednesday. His sister made a plea for his release after two dual nationals were allowed to leave Iran.

The United Kingdom paid a $530 million old debt to Iran before two dual nationals were released last week and Tahbaz was also supposed to go on furlough according to the deal. He was jailed in 2018 and sentenced to 10 years on trumped-up charges of espionage, like many other dual-nationals and foreigners imprisoned by Iran.

Britain's foreign ministry said on Friday it had been told by Iran that Tahbaz, 66, had been taken back to Evin prison in order to fit an ankle bracelet and that the British government hoped he would be allowed out in coming hours.

"Morad has now been moved from Evin prison to a residential location in Tehran," a Foreign Office spokesperson said in a statement on Monday.

"We ... continue to lobby the Iranian authorities at the highest levels to allow him to return home immediately, as the Iranian government committed to doing."