The husband of a British-Iranian charity worker who has been held in Iran for more than a month has asked the UK authorities to get her home.
Nazanin Zaghari-Ratcliffe, 37, was arrested on 3 April at an airport after visiting her family on holiday.
Richard Ratcliffe says she has been held in solitary confinement ever since over an issue of "national security".
Their 22-month-old daughter, Gabriella, is also still in Iran because her passport has been taken, he says.
Mr Ratcliffe, from north London, says his wife had been about to return to the UK when she was detained by the Iranian Revolutionary Guard and taken to an unknown location in Kerman Province, 621 miles (1,000km) south of Tehran.
He says Mrs Zaghari-Ratcliffe, who works as a project coordinator for the Thomson Reuters Foundation, has not been allowed access to a lawyer or to see her daughter and has not been able to call out of the country to speak to him.
According to him, she has not been charged but has been forced to sign a confession "under duress", despite not knowing what she was confessing to.
Mr Ratcliffe told the BBC there was nothing in her work or personal background to explain why she was detained, saying she had travelled to the country before without any problem.
He said her family in Iran heard nothing after her arrest for three days, when she was allowed to phone and tell them she was safe.
They were told she would be released within a couple of days, he said, but after they heard nothing they later learned she had been transferred to southern Iran.
The Thomson Reuters Foundation, the charitable arm of the news agency Thomson Reuters, runs projects around the world - including providing media coverage of under-reported areas and free legal assistance - but does not work in Iran.
Mr Ratcliffe said: "It is hard to understand how a young mother and her small child on holiday could be considered an issue of national security. She has been over to visit her family regularly since making Britain her home.
"The cruelty of the situation seems both outrageous and arbitrary - that a young mum and baby can be treated as some national security threat is absurd, far outside any reality our family was familiar with."
Gabriella, a British citizen, has had to stay with her grandparents in Iran because she cannot return to the UK without her passport.
Mr Ratcliffe, who has been advised to stay away from the country, told the BBC he was only able to speak to his daughter over Skype.
He said: "She is clearly struggling and adapting and waking up in the middle of the night screaming and looking for mummy and looking for daddy, but she is also playing with her cousins and she is safe."
An online petition set up to urge Prime Minister David Cameron to step in has attracted more than 3,000 signatories and has been sent to Mr Cameron and Iran's Supreme Leader, Ayatollah Ali Khamenei.
Mr Ratcliffe said he was going against the advice of the Foreign Office in speaking publicly about his wife's detainment because he hoped public pressure might help towards securing her release.
He added: "I am pleading to the British authorities, now that delegations are travelling between the two countries to improve trade and understanding, that all efforts are made to bring my wife and daughter home as quickly as possible and to get Nazanin out of solitary confinement immediately."
A spokesman for the Thomson Reuters Foundation said Mrs Zaghari-Ratcliffe, who is in charge of grant applications and training, had "no professional dealings with Iran whatsoever".
He added: "We are in close contact with her family. We cannot understand the reason for her detention and hope the matter will be resolved as soon as possible."
A Foreign Office spokeswoman said: "We have been providing support to the family of a British-Iranian national since we were first informed of her arrest, and will continue to do so."