Nazanin Zaghari-Ratcliffe: What is Iran jail case about?
It has been 20 months since jailed mother Nazanin Zaghari-Ratcliffe was detained at an Iranian airport while travelling home to London with her young daughter.
Since her arrest on 3 April 2016, the British-Iranian charity worker has been sentenced to five years in prison - for allegedly plotting against the Iranian government.
She maintains her innocence, saying she was on holiday in Iran visiting family.
Her supporters are hopeful of movement after Foreign Secretary Boris Johnson visited Tehran and met his counterpart as well as President Hassan Rouhani, and pressed for her release on humanitarian grounds.
Here are the details of the case.
Who is Nazanin Zaghari-Ratcliffe?
Mrs Zaghari-Ratcliffe, 38, has dual British and Iranian citizenship, and before her arrest lived in London with accountant husband Richard Ratcliffe.
She worked as a project manager for the charity Thomson Reuters Foundation and was previously employed by BBC Media Action, an international development charity.
She says she took her daughter Gabriella, three, to Iran in March 2016 to celebrate the country's new year and visit her parents.
What is she accused of?
Iranian authorities allege Mrs Zaghari-Ratcliffe was plotting to topple the government in Tehran - but no official charges have been made public.
Iran's Revolutionary Guards said she was visiting Iran leading a "foreign-linked hostile network".
Both her employers, Thomson Reuters Foundation and BBC Media Action, have issued statements saying she was not working in Iran but was on holiday there.
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Mr Ratcliffe said he had asked his wife what the charges were during a phone call in 2016, and a nearby prison guard had said: "National security charges".
Mr Ratcliffe said she could face a second charge of "spreading propaganda," which could add another five years to her sentence.
The new charges come after Foreign Secretary Boris Johnson suggested Mrs Zaghari-Ratcliffe had been "teaching journalism" in Tehran, which he later apologised for.
What happened after her arrest?
- April-June 2016: According to Mr Ratcliffe, his wife was subject to "intense interrogation" for the first two months of her imprisonment and kept in solitary confinement
- September 2016: Mrs Zaghari-Ratcliffe is sentenced to five years in prison in Tehran's Revolutionary Court
- January 2017: She loses an initial appeal against her sentence
- April 2017: Mrs Zaghari-Ratcliffe loses a final appeal in Iran's supreme court to overturn her sentence
What has Mrs Zaghari-Ratcliffe said?
Mrs Zaghari-Ratcliffe, who maintains her innocence, mostly speaks publicly through her husband, who regularly calls her in prison.
According to Mr Ratcliffe, she says she misses Gabriella "all the time" and is in a "pretty fragile" state of mental health. Doctors recently found lumps in her breasts, which were not found to be cancerous, he said.
She recently told her husband and supporters over the phone during a rally in London: "It has been really difficult for me to be in prison."
What has the UK government done?
Prime Minister Theresa May "raised concerns" in the early stages of the case with Iran's president, Hassan Rouhani. The UK Foreign Office said it was "deeply concerned" by her sentence - and said ministers would continue to raise the case with Iranian officials.
But the British government is in difficult position - Iran refuses to recognise dual nationals and denies them access to consular assistance.
Soon after Mr Johnson's comments, which suggested Mrs Zaghari-Ratcliffe was training journalists, Iran moved to double her prison sentence. The foreign secretary later stated in the Commons that he had "no doubt" she was on holiday and had called Tehran to clarify.
Mr Johnson visited Tehran and met his counterpart as well as President Hassan Rouhani, and pressed for her release on humanitarian grounds, in early December 2017.
The Foreign Office is now considering whether it will give diplomatic protection to Mrs Zaghari-Ratcliffe - making the case a formal, legal dispute between Britain and Iran.
What are the politics behind her case?
Mrs Zaghari-Ratcliffe's five-year-sentence was handed down on 6 September - one day after the UK appointed an ambassador to Iran for the first time since 2011.
Mr Ratcliffe cites the timing as proof his wife is being held as a political bargaining chip.
BBC diplomatic correspondent Caroline Hawley said London and Tehran do not see eye-to-eye on Iran's role in the wider Middle East or on human rights.
Iran's Revolutionary Guards are hardliners, opposed to Iran's nuclear deal struck by moderates with the west in 2015. And in 2009, Britain was accused of fuelling unprecedented street protests.
How is the campaign to free her progressing?
Mr Ratcliffe has petitioned the UK government to help free his wife, making numerous TV appearances and visiting Downing Street.
Actress Emma Thompson turned out to a march he organised in London in November urging her release - despite suffering a bout of pneumonia. "I can't not come to speak," she told BBC News. "Because I'm free. I'm free."
Tulip Siddiq, the couple's constituency MP, said the latest charges brought against her were "an outrage and must not be allowed to stand".
Mr Ratcliffe met with Mr Johnson in November and discussed the possibility of a joint trip to Iran before the end of the year - but Mr Johnson went alone.
Others imprisoned in Iran
An estimated 12 to 30 dual nationals from Britain and other western nations are imprisoned in Iran accused of espionage, although exact numbers are unclear. Many of their relatives think they are being held for political reasons.
Another British-Iranian national to be arrested is Kamal Foroughi, 78, who was working in Tehran as a consultant but thrown in jail in 2011 and later accused of spying.
Speaking to the BBC in 2015, his son Kamran said the family still did not understand why he was being held.
Chinese-American student, Xiyue Wang, has been held since the summer on unspecified espionage charges. An Iranian Appeals Court in September upheld a 10-year prison sentence against the doctoral student.