Iran is set to allow what is believed to be its first transsexual marriage after the would-be bride asked a court to override her father's opposition to the match.

The woman, named only as Shaghayegh, told Tehran's family court that she wanted to wed her best friend from school, who had recently undergone a sex-change operation to become a man, but was unable to obtain her father's blessing, as legally required.

Now her father has agreed to permit the union on condition that the male partner, Ardashir, who was previously a woman called Negar, undergoes a medical examination intended to prove it would be a proper male-female relationship.

The case comes against the backdrop of Iran's notoriously repressive policies on homosexuality, which is illegal under the country's strict theocratic code. Gay rights groups have accused the authorities of executing homosexuals, although officials deny the charge.

The father's change of heart came after he was summoned to court to explain his opposition. He told the judge, Alireza Sedaghati, that he had been driven by "fear of humiliation".

"During the last several years, Ardashir came to our house many times and all the neighbours and relatives know him as a girl," he said.

"Now she has changed gender and turned into a man, I can't sit and watch my daughter's friend turning into my son-in-law."

But he relented in the face of his daughter's insistence that she be allowed to wed Ardashir.

"Ardashir and I have been together since adolescence and know each other very well. This familiarity can make us happy," she told the court.

Etemaad newspaper reported that the two had been friends for 12 years after meeting at school and had later studied at the same university, where their close relationship had been well known to fellow students.

After graduating, Negar changed sex under Iran's Islamic laws which deem transsexuals religiously permissible, in contrast to the blanket ban on homosexuality, which is considered a sin.

Iran carries out more sex change operations than any other country apart from Thailand after the late Ayatollah Ruhollah Khomeini, spiritual leader of the 1979 Islamic revolution, issued a religious fatwa approving the practice, which has government funding. Critics have suggested that some of those changing sex are not true transsexuals but gays or lesbians who feel forced into the operation by social pressure.