Charity worker Nazanin Zaghari-Ratcliffe, who was jailed in Iran in 2016 after being accused of spying, has been temporarily released from prison for three days.
Her British husband Richard Ratcliffe said Ms Zaghari-Ratcliffe, a British-Iranian citizen, was with family in Damavand and had been reunited with her daughter Gabriella, four.
He said: "The Free Nazanin campaign is very pleased to confirm that Nazanin was released from Evin prison on furlough this morning.
"Initially the release is for three days - her lawyer is hopeful this can be extended. She is currently with her family in Damavand.
"This was a very happy surprise after a number of false dawns recently, which had been increasingly unsettling."
Foreign secretary Jeremy Hunt tweeted that she should be "permanently released".