Image caption Nazanin Zaghari-Ratcliffe, pictured with her husband Richard and daughter Gabriella, has been held in Iran for more than two months

The father of a toddler stuck in Iran without either of her parents has sung Happy Birthday to her via Skype at a campaign event.

Richard Ratcliffe, of north London, also left a card at Iran's embassy for Gabriella's second birthday.

His wife Nazanin Zaghari-Ratcliffe, 37, was arrested on 3 April at an airport in Iran after visiting her family.

He says she has been held without charge, while Gabriella remains in Iran because her passport has been taken.

Mr Ratcliffe, who has been advised to stay away from Iran, says his British-Iranian wife has been held in solitary confinement over an issue of "national security".

Their daughter, a British citizen, has had to stay with her grandparents in Iran because she cannot return to the UK without her passport. Under Iranian law only her father or mother can take the toddler home.

'Powerful support'

More than 759,000 people have signed a petition calling for Prime Minister David Cameron to intervene in the case.

The Free Nazanin Campaign event was the culmination of its birthday card campaign, which has seen thousands of people sending cards for Gabriella via Iranian embassies around the world.

Mr Ratcliffe said: "Today is quite a happy day. Her birthday is tomorrow - and that will be a sad day."

Support from the public was "really really powerful" and an "important factor in keeping me going", he said.

"I look at all these lovely comments, and some of them are so beautiful they'll bring tears to my eyes: the energy and the love and the kindness that's out there," he added.

Image copyright Free Nazanin Image caption Mrs Zaghari-Ratcliffe has not been able to see her daughter since she was arrested

The 41-year-old plans to spend Saturday with his parents, when they will call Gabriella, whose grandparents in Iran are throwing a party.

Mr Ratcliffe said: "Sometimes you speak to her and she just gets really upset and keeps asking for her mum, which is the most heartbreaking part."

Mr Ratcliffe said 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 said Mrs Zaghari-Ratcliffe, who works as a project co-ordinator for the Thomson Reuters Foundation, had not been allowed access to a lawyer or to see her daughter.

'Confession under duress'

According to him, she has not been charged but had been forced to sign a confession "under duress", despite not knowing what she was confessing to.

Mr Ratcliffe previously told the BBC there was nothing in her work or personal background to explain why she had been detained, saying she had travelled to the country before without any problem.

He said her family in Iran had heard nothing after her arrest for three days, until she had been allowed to phone and tell them she was safe.

Image copyright Free Nazanin Image caption A petition calling for Prime Minister David Cameron to intervene has attracted more than 759,000 signatories

They were told she would be released within a couple of days, he said, but they later learned she had been transferred to southern Iran.

Mr Ratcliffe has said he is going against the advice of the Foreign Office in speaking publicly about his wife's detainment because he hopes public pressure might help secure her release.

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."