A British-Iranian woman has been reunited with her family after being granted a three-day release from prison in Iran.
Nazanin Zaghari-Ratcliffe was jailed for five years in 2016 after being convicted of spying, which she denies.
She said she was "overwhelmed" and it would be "awesome" for her four-year-old daughter to "have a mummy again".
Foreign Secretary Jeremy Hunt said her imprisonment was a "gross injustice" and the release should be permanent.
The Free Nazanin campaign group said a three-day release was "standard practice" ahead of lengthier times out of jail and her lawyer was due to apply for an extension on Saturday.
Her husband Richard Ratcliffe said her temporary release was a "happy surprise" and she is with family in Damavand.
Mrs Zaghari-Ratcliffe, who works for the charity Thomson Reuters Foundation, was arrested at Tehran airport after visiting her family on holiday.
Iranian authorities have accused her of espionage but she insists the visit was to introduce her daughter to her family.
In a statement issued by the Free Nazanin campaign, Mr Ratcliffe said his wife was still in her nightclothes when she was given 10 minutes notice on Thursday morning that she was being released until Sunday 26 August.
The campaign group said the possibility of release had been discussed for several weeks but there had been "a number of false dawns".
She was released on condition she does not:
- Conduct interviews with the media
- Visit a foreign embassy, especially the UK's
- Attempt to leave Iran
Free Nazanin said Mrs Zaghari-Ratcliffe and her father have both separately promised she will obey the rules.
Analysis - No explanation from Iran
By BBC World Affairs correspondent Richard Galpin
It was around two weeks ago that Nazanin Zaghari-Ratcliffe first heard she might be allowed to leave Evin prison for a few days so she could see her family and in particular her four year-old daughter Gabriella.
After several false alarms she is now reunited with them.
So far there's been no official announcement by the Iranian authorities explaining why they decided to grant her this respite now.
One theory is that it's a gesture during the Islamic festival of Eid.
Another possibility is that the appointment of a new foreign secretary, Jeremy Hunt changed the diplomatic dynamics.
Although earlier this week, Mr Hunt admitted he had not yet decided whether to grant Mrs Zaghari-Ratcliffe diplomatic protection as a means of improving her chances of being released, much to the frustration of her family.
In comments issued by the campaign, Mrs Zaghari-Ratcliffe said she "wasn't expecting it at all".
She said: "It will be just awesome for Gabriella to have mummy home finally. We can play with her dolls house and she can show me her toys.
"The thought of brushing her hair, and giving her a bath; of being able to take her to the park, and feed her, and sleep next to her - it just kills me. It is still so hard to believe.
"I was so emotional to see my grandmother today. I cried so much. I felt so overwhelmed.
"It felt like this really could be the beginning of the end."
Mr Ratcliffe has campaigned for her release since she was jailed and met Foreign Secretary Jeremy Hunt earlier this month, who vowed to do "everything we can to bring her home".
The campaign thanked "all those involved in making this possible in Tehran and London, and the new foreign secretary".
Mr Ratcliffe said: "Furlough is not full freedom - we want her home, not just on holiday from prison - but after 873 days it is a massive step."
Mr Hunt called the release "really good news" with credit going to the "tireless campaigning" of Mr Ratcliffe and the family's friends.
He also thanked the Iranian authorities "whilst not forgetting that she should not be in prison in the first place".
"Nazanin is innocent," the foreign secretary added.
How did the release happen?
According to Free Nazanin, Mrs Zaghari-Ratcliffe was told she had 10 minutes to get ready to leave, with her cellmates gathering around to see her off.
Once dressed, she was taken to the door and, following a detailed search of each item she was taking out of prison, she was taken from the ward to the main entrance of Evin prison in Tehran.
Unknown to her, her family had been called by the prison authorities an hour earlier but they were out of Tehran on holiday in Damavand about 46 miles (74km) away to celebrate Eid.
Her father was on his way back to Tehran when she was released.
Prison authorities asked her not to stand outside the prison so she crossed a nearby bridge where she asked a family waiting for another inmate to be released if she could borrow their phone to call her brother, who was still in Tehran.
He arrived within 10 minutes and she called her husband and then the British embassy before her father arrived.
The trio then travelled to the family celebration where they arrived just in time for lunch.
A spokesman for the Foreign and Commonwealth Office said: "We remain very concerned about all our dual nationals detained in Iran, and continue to make decisions in line with what we believe will produce the best outcomes in their cases.
"We do not think it is in the best interests of any of our dual national detainees to provide a running commentary on individual cases."
The Iranian ambassador in London said Iran's Foreign Ministry is in contact with the country's judiciary to help Mrs Zaghari-Ratcliffe on "humanitarian grounds".
Hamid Baeidinejad made the comment in response to a Twitter user who asked if he would intervene to release her permanently from prison.
Mr Baeidinejad posted a photo of the mother and her four-year-old daughter reunited describing it as a "lovely picture".
Mrs Zaghari-Ratcliffe's family have previously criticised the UK government for not negotiating her release.
Boris Johnson provoked consternation in November last year when he told MPs that Mrs Zaghari-Ratcliffe had been "training journalists" in Iran.
The then-foreign secretary later stated in the Commons that he had "no doubt" she was on holiday and had called Tehran to clarify after the Iranian authorities moved to double her sentence.