Kadhimiya is the location of one of Shia Islam's most important pilgrimage sites. Millions of people come from all over the world to visit the mosque commemorating the martyrdom of the death, in the 8th Century, of Moussa al-Kadhim, the seventh of the 12 Shia imams.

Dotted among the bustling market stalls surrounding the shrine are dozens of offices where couples go to get married under Islamic law, or Sharia, before appearing before a judge to obtain an official marriage certificate. Most couples are seeking permanent marriages. But some are looking for mutaa marriages.

Despite being illegal in Iraq, the BBC found that mutaa marriages were widely available in Kadhimiya. Out of 10 clerics approached by a BBC undercover reporter, eight said they performed them. Of those eight, we had further conversations with two who agreed to approve them for girls as young as nine.

“I can take a photo of her and send you her photo... Then when you come back she's yours” Sayyed Raad

It is impossible to quantify exactly how widespread the practice of under-age mutaa marriage is in Iraq.

Ghaith Tamimi, a former senior Shia cleric from Karbala, said he witnessed thousands of mutaa marriages but none with children. He acknowledged that Sunnis also enter into informal marriages, but said the fact that the Shia clerics are closer to those in power means they can act with impunity.

The BBC decided to investigate after it was contacted by concerned members of communities in Iraq.

In the marriage offices in Kadhimiya, clerics approached by the BBC undercover reporter elaborated on their practice.

“You can marry a woman for half an hour, and as soon as it's over, straight away you can marry another one,” says one of these clerics, Sayyed Raad, who uses the honorific title of Sayyed because he claims descent from the Prophet Muhammad.

He also says he can arrange a “first class” hotel suite for the reporter and his mutaa marriage bride, despite it being illegal for a couple to rent a hotel room in Iraq unless they are married under civil law.

Some of the clerics also appear unconcerned that the bride in question is very young.

The legal age for marriage in Iraq is 18, although judges are allowed to permit girls as young as 15 to marry in “urgent” cases. Sharia, meanwhile, says that girls are allowed to marry once they have gone through puberty.

Clerics are required by Sharia to obtain parental consent if the girl is under-age. But Sayyed Raad is happy to officiate even when our reporter pretends the girl in question is a 13-year-old virgin.

Instead he just advises against taking the girl's virginity. He suggests anal sex as an alternative. And he is happy to conduct the ceremony over the phone, with the girl not even present.

He charges our undercover reporter $200 for the minutes-long ceremony.

He even agrees to procure our reporter another girl for a later date.

“I can take a photo of her and send you her photo. Then you agree with her. Then when you come back she's yours.”

Sayyed Raad brings another young woman available for mutaa marriage to meet our undercover reporter. The cleric says she is available to spend the night with him for $300. When the reporter says he doesn't want to go ahead with the mutaa marriage, Sayyed Raad then offers to use her to find the reporter a younger bride.

“Maybe she can find me a girl who is 14, 15, 16 years old. I will go with her to check the girl and if she's young I will bring her to you.”

In Karbala, a Shia holy city 120km [75 miles] south of Baghdad, the BBC asks Sheikh Emad Alassady, the most senior cleric in the city's Sharia marriage office in Karbala mosque, whether he approves of the practice of mutaa marriage. He says although allowed in Sharia he would never officiate one.

“The culprit would be sentenced to prison, even if he was a cleric” he says.

But in the streets around the shrine, some clerics are giving very different advice.

Cleric Sayyed Mustafa Salawi says he would be happy to officiate a mutaa marriage between the reporter and a girl the reporter pretends is 12 years old. He is not concerned that the bride is young.

“Nine years-old plus, there's no problem at all. According to Sharia, there is no problem... Do what you desire.”

And when contacted again, a few days later, to find out if he could provide another bride, he is happy to provide a choice of women.

“They won't send photos but when you see them face to face, they're good girls, beautiful girls. If you don't like her, there will be a second and a third and so on.”

The BBC later approached the clerics it had filmed undercover to ask for their response. Sayyed Raad denied he performed mutaa marriages at all. The others did not respond.

Sayyed Raad had said he was a follower of Grand Ayatollah Ali Sistani, Iraq's most influential Shia cleric.

The BBC approached Ayatollah Sistani's office in the holy city of Najaf with the reporter’s evidence, and asked him to clarify his stance on mutaa marriages.

“If these practices are happening in the way you are saying then we condemn them unreservedly,” his office says in a statement. “Temporary marriage is not allowed as a tool to sell sex in a way that belittles the dignity and humanity of women.

“A guardian of a girl should not permit her marriage without her consent… and she is not supposed to marry if it’s against the law, which could bring troubles to her.”

Like some other Shia leaders in Iraq, the 89-year-old Ayatollah Sistani has in the past - in a book published 25 years ago called The Path of the Righteous - written that if a child under nine were promised in marriage or temporary marriage, sexual touching was religiously permitted.

In the statement to the BBC, the ayatollah’s office said: “times had changed and it had been erased from his current books”.

Ali, a professional man in his 40s, is one of those who uses clerics to source him women and girls for mutaa marriages. “It doesn't count as a sin. It is available and it is cheap and it's fine to do it,” he says.

“Lots of clerics do [facilitate] it, but I only use two because they provide me with all the girls I need,” he says.

“The cleric has a photo album, sometimes several girls are sitting in his office. If you like one of them, you can take her. If you don't, your second choice is the photo album.”

Ali says he personally prefers girls who are 16 and older because they are more experienced and more affordable than the younger girls. The 12-year-olds, he says, are “fresh” and therefore more expensive, earning the clerics as much as $800 per contract.

Rusul agrees it is the virgins that are in demand.

“There are clerics who look for young virgin girls because many customers want them, they are more desired, and people pay more for them. This is happening to many girls - not just a few.”

She says 20 is the cut-off age for girls working for the clerics.

Losing your virginity outside marriage carries considerable risk in the country, as it is seen by some Iraqis as tainting family honour.

Mona was just 14 when she was persuaded into a mutaa marriage with an older man who followed her home from school.

Now several years older, Mona is under pressure from her family to marry, and is terrified her future husband will find out she's no longer a virgin. She says that her uncle killed her cousin just for having a boyfriend. She says she is contemplating suicide.

“I have no way out. If I feel under any more pressure, I will do it,” she says.

Since the BBC spoke to Mona, she has run away from home.

But it's not just girls who are vulnerable to the potentially exploitative tool of mutaa marriages.

Rana, in her 20s, was divorced by her husband after she fled to Baghdad five years ago, after militants from the Sunni jihadist group Islamic State [IS] overran her home city.

“For us, a cleric is something very special, but then you discover that this guy wearing a turban is a cheat” Rana

When she met someone else she was delighted by his proposal. She had assumed it would be a permanent union. She didn't bother to read the contract because she trusted her husband.

Even if she had, she might well have missed the fact that it was a mutaa marriage, since the contract is the same as a regular Sharia marriage contract - the cleric just writes “mutaa” in brackets, a detail that is easy to miss.

“We had three of the happiest days of my life - ordering food. He cherished me. When you're broken, and someone comes and gives you hope, it's very precious.”

But then her husband took her out shopping, and without warning vanished.

When her family discovered that her marriage had only been temporary, they rejected her. Although mutaa marriages are sanctioned by Shia clerics, it's seen as dishonourable - essentially prostitution - by many sectors of Iraqi society, both Shia and Sunni.

“When you get married, you feel secure, you're happy. He's your husband, you believe you have a future, but it turned out it was all a lie. For us, a cleric is something very special, but then you discover that this guy wearing a turban is a cheat.”

Some clerics defend mutaa marriage as a way for widows and divorcees to obtain an income, as the woman gets a dowry. They also say that women have sexual desires and want a religiously-approved means of sleeping with men.

Rusul says this is a false notion.

“Maybe some desire this, but I don't think many people would like to take that road if they are financially secure. Why would a teenager want to do this?”

Ayatollah Sistani’s office told the BBC the abuses we have witnessed are because the authorities are not enforcing the law.

An Iraqi government spokesman told the corporation that it is difficult for the authorities to act “if women don’t go to the police with their complaints against clerics”.

But for girls like Mona, who don’t want their families to find out about their mutaa marriages, going to the police seems impossible.

There are no statistics for how many mutaa marriages are being conducted but anecdotal evidence suggests they have become more common in the wake of the US-led invasion of Iraq in 2003.

The invasion toppled Saddam Hussein's nominally secular government, and ended the political and economic dominance of Iraq's Sunni minority and the persecution of the country's Shia majority. Since then, Iraqi Shias have sought redress and reversed the imbalance of power. The country's Shia clerical establishment now holds enormous sway.

Though it isn't possible to verify all the details of Rusul's story, sources have confirmed that many elements of her account are similar to those of other girls who have been exploited by clerics in this way. Other girls, for example, have spoken of being given contraceptive injections.

Rusul regrets the day she ever unwittingly took this path.

“The moment a girl starts doing this, her life is ruined.”