A British man has begged the Government to intervene and help free his charity worker wife after she was taken captive in Iran and separated from her infant daughter.
Nazanin Zaghari-Ratcliffe, who has dual British-Iranian nationality, was detained by the Iranian Revolutionary Guard on April 3 at an airport as she tried to return to the UK after visiting her family in Iran.
The 37-year-old is being held in solitary confinement in an unknown location in Kerman Province, 1,000km south of the capital Tehran.
Her daughter Gabriella, who is 22 months old and has British citizenship, is being cared for by her grandparents.
But she has had her passport confiscated, leaving her stranded in the country.
An online petition set up to urge Prime Minister David Cameron to step in said: "Nazanin has not been allowed access to a lawyer or her daughter.
"She has not been able to call out of the country to speak to her British husband, Richard Ratcliffe. The Red Cross have not been able to make contact.
"There have been no charges. Nazanin has informed her family that she has been required to sign a confession under duress, its content unknown.
"Her family have been informed that the investigation relates to an issue of 'national security'."
Mr Ratcliffe added: "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."
Mrs Ratcliffe is a project manager for the Thomson Reuters Foundation, which delivers charitable projects around the world. It does not work in Iran.
The petition, which has been sent to Mr Cameron and Iran's Supreme Leader, Ayatollah Ali Khamenei, has attracted more than 3,000 supporters.
Family member Barbara Ratcliffe said: "The whole family is frantically worried about Nazanin's safety.
"We have been given false information and hope that she would be detained for a couple of day(s) more - and that was a month ago and still no Naz. We desperately need both Naz and Gabriella home."
A Foreign Office spokeswoman said: "We have been providing support to Mrs Zaghari-Ratcliffe's family since we were first informed of her arrest and will continue to do so."
Mr Ratcliffe told the BBC there is nothing in his wife's work or personal background to explain why she was detained 36 days ago, 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 heard nothing, later learning she had been transferred to southern Iran.
Mr Ratcliffe said: "She was on holiday, she is a British charity worker, she works for an organisation that doesn't do anything in Iran, she has been to Iran four times in the past two years without any problems, she is there with a young baby."
He said he has not had any direct contact from the Iranian authorities, but two weeks after his wife's arrest they called her father to confirm they had detained her. Officials contacted him again last week to explain it was an issue of national security.
Mr Ratcliffe said he was managing to speak with his young daughter every day via 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."