Nazanin Zaghari-Ratcliffe has returned to prison in Iran voluntarily following a three-day release, her husband says.
The British-Iranian charity worker was reunited with her family, including her four-year-old daughter, during the temporary release.
She applied for an extension, but it was denied, Richard Ratcliffe said.
The charity worker chose to return to prison “with her head held high” rather than be “dragged out” in front of her child, he said.
Ms Zaghari-Ratcliffe, who works for the Thomson Reuters Foundation, was jailed for five years in 2016 after being convicted of spying, which she denies.
She was was arrested at Tehran airport after visiting her family on holiday. She insists the visit was to introduce her daughter Gabriella to her relatives.
Mr Ratcliffe said her lawyer had been initially confident that his appeal for an extension to the release would be granted.
Having received mixed messages throughout the day, she was then told she had to return to prison by sunset on Sunday as the necessary permit had not been signed off.
A picture of her saying goodbye to her daughter was posted on the Free Nazanin campaign’s Twitter account.
In a statement, Mr Ratcliffe said: “After discussion with her family in Iran, Nazanin decided that she would go into prison.
“She did not want to be dragged out of the house in front of her baby, but would walk into prison with her head held high.”
He said their daughter Gabriella, who has been staying with family in Iran, cried when she realised her mother was leaving.
He said: “Nazanin waited for Gabriella to wake up before saying goodbye, and left her family home to return to Evin prison.”
Mrs Zaghari-Ratcliffe, from Hampstead, north London, told her daughter “the next time she saw her, it would be forever, not just for a few days – for proper freedom, not just for furlough” and that “next time they will go back to London to be with daddy”.
The Foreign Office said in a statement: “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.”
Her husband had believed she would not have to go back into prison.
“I still find it an extraordinary decision,” he said in the statement. “I did not believe after all the effort it took to get out, it would only be for three days.”
Mrs Zaghari-Ratcliffe told him she was concerned about the impact of the latest development on her young daughter, saying: “You can’t send a small child her mummy, and then take her away again after three days. It is cruel. It is beyond cruel.”
She had only been given 10 minutes’ notice that she was being released on Thursday, the campaign said. The possibility of a temporary release had been discussed previously, but there had been a number of “false dawns”.
The campaign group said on Thursday that a three-day release was “standard practice” ahead of lengthier times out of jail.
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”.
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.