The case of Ghoncheh Ghavami, a law graduate from London, has been surrounded by confusion since her lawyer said earlier this month that the 25-year-old had been sentenced to a year in prison for committing propaganda against the Iranian regime.
That reported jail term has been denied by judicial authorities, but in a fresh twist Ghavami's mother Susan Moshtaghian said a judge had agreed to let her daughter leave jail on bail of 1,000,000,000 Iranian rials (around $30,700).
"Right now, my daughter is freed until the Court of Appeal issues the final verdict," she told the ISNA news agency in a report in which she also appeared to confirm the initial prison sentence.
Saying that the one-year jail term and an additional two-year restriction on leaving Iran had been communicated to her, Moshtaghian added: "My daughter merely defended herself in the preliminary court and insisted on herself being innocent.
"We hope she'll be acquitted by the appeal court of the charges."
Ghavami was detained outside Azadi ("Freedom" in Persian) Stadium in the capital on June 20, having gone there to watch a volleyball match.
She was refused entry as women are not allowed to watch male athletes in the Islamic republic.
Officials have said that Ghavami was arrested for security reasons unrelated to the sporting event.
Her release on bail came after Moshtaghian went to court on Sunday to seek her release on medical grounds, but by allowing the young woman out on bail the judge said "there would be no need for sick leave".
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Ghavami is said to have developed gastrointestinal problems after going on hunger strike twice. She has also lost weight since being jailed.
Her brother, Iman, told AFP separately that she "was released on bail just a couple of hours ago and she will stay with my parents" in Tehran.
However, he said there remained the possibility that she would be returned to jail, as the Court of Appeal must still decide how she must serve her full sentence.
"She might go back to prison," he said in London, noting that efforts to impose additional charges against his sister had failed and she was in the end sentenced for "propaganda against the regime".
"It was unexpected that she was released, it was out of the blue," he said, adding that he had managed to speak to his sister for "just a few seconds -- I think she sounded happy".
But he insisted: "Everyone knows that she didn't do anything. She shouldn't have been in prison for the past five months anyway."
Female fans and women journalists were told they could not attend the volleyball match, leading to a brief protest.
Ghavami was initially released after a few hours, but was rearrested days later at a police station when she went to reclaim items that had been confiscated near the stadium.
Her case has drawn international attention and been described by Amnesty International as "appalling".
The British Foreign Office has raised concerns about the court's ruling as well as "grounds for this prosecution, due process during the trial and Miss Ghavami's treatment while in custody".
Ghavami's family have said that at least 41 days of her detention before trial were spent in solitary confinement.
The case comes with Tehran under pressure over its human rights record, after the easing of Iran's international isolation following last year's election of moderate Hassan Rouhani as president.