Nazanin Zaghari-Ratcliffe, the British-Iranian woman detained in Iran nearly six years ago, is on her way to the UK, her MP has said.
Mrs Zaghari-Ratcliffe was at the airport in Tehran, Tulip Siddiq told BBC News.
She is in a holding room with fellow British-Iranian detainee Anoosheh Ashoori, she said.
Mrs Zaghari-Ratcliffe was arrested in 2016 – accused of plotting to overthrow Iran’s government, which she denied.
Mr Ashoori was arrested in 2017 and accused of spying, a claim he denied.
Mrs Zaghari-Ratcliffe had been under house arrest and was given her UK passport back this week.
Her husband Richard Ratcliffe, who lives with their six-year-old daughter Gabriella in Hampstead, London, has not yet commented. He had campaigned for her release, including by going on hunger strike in October last year.
Ms Siddiq, Labour’s MP for Hampstead and Kilburn, told BBC News that she had spoken to Mr Ratcliffe.
Mrs Zaghari-Ratcliffe was at the airport with her passport, she said, but remained “under the control of the Iranian Revolutionary Guard”.
She said a deal to secure her freedom had not “been completed yet”.
“I won’t rest until she is on British soil, in West Hampstead, in her house,” she added.
Mrs Zaghari-Ratcliffe’s sister-in-law Rebecca Ratcliffe told BBC News it was an “emotional day”.
“It feels like we’re on the home run now but until she leaves that airport we can’t believe it,” she said, adding that she had also spoken to Mr Ratcliffe.
She said Mrs Zaghari-Ratcliffe had been picked up and taken to the airport with her parents, who were not allowed in a holding room with her because she was “still under Iranian control in the airport”.
“She’s still not free. But it definitely feels like she’s about to be,” she said.
Earlier Ms Siddiq said Mrs Zaghari-Ratcliffe had been “dreaming” about the day she could return to the UK.
Iranian media is also reporting that she had been transferred to the airport.
A £400m debt relating to a cancelled order for 1,500 Chieftain tanks dating back to the 1970s had been linked to the continued detention of Mrs Zaghari-Ratcliffe and other UK-Iranian dual nationals held in the country – although the government has previously said the two issues should not be linked.
Ms Truss told the BBC on Wednesday the debt was “legitimate” and that the government was “looking for ways to pay” it.
Labour leader Sir Keir Starmer said it was “an incredible moment” for Mrs Zaghari-Ratcliffe and her family after an “unimaginable ordeal”.
He added that there would be questions to be answered about “what happened along the way”, but at present his thoughts were with the family.