When Yisrael Amir got married, he and his bride stood under the chupah, the traditional Jewish wedding canopy, surrounded by members of their community.

But what should be a couple's happiest day was for them a nightmare.

Yisrael and his wife, Malke (not her real name), were both 16 and had met there and then for the first time.

The marriage had been organized by leaders of the group which they had been brought into as children.

The group is Lev Tahor, Hebrew for Pure Heart, which claims to follow a fundamentalist version of Judaism.

Former members though, along with an Israeli court among others, say it is nothing but a cult.

"We had no choice," Yisrael, now 22, tells me as we sit and talk in the back yard of his aunt's house, just south of Tel Aviv.

"The rabbi called me into his office and said, 'Next week you're getting married. If you refuse you get punished'.

"My sister was 13 and they forced her to marry a 19-year-old. She was crying. She cried so much they punished her by banning her from speaking for a year.

She could not say a word - not ask for food, not ask for the toilet, nothing."

This was part of life at the group's compound in Guatemala, where the legal age for marriage is 18 for both men and women.

Most of Lev Tahor had settled in the Central American country in 2013 after fleeing Canada, where it faced allegations of child abuse. It has denied these claims.

Yisrael says his sister could not speak properly after the year-long punishment ended.

Such treatments are part of a catalogue of alleged abuses meted out by leaders and those in positions of authority in the group, according to Yisrael and other former members.

These reportedly include beatings for minor infractions, with children forced to thank their tormentors for hitting them.

But, according to Yisrael, there was much worse.

"I saw every day Shlomo Helbrans [the founder of Lev Tahor] and another leader take boys in their room, boys as young as eight, then afterwards he sent them to the mikveh [ritual bath used for purification]. I didn't understand what he did with them. Now I know."

Yisrael says boys and girls told him they were sexually abused - and raped.

The BBC tried to speak to alleged child victims of rape who have left the group, but none were willing to talk. A US-based support group, Lev Tahor Survivors (LTS), told the BBC there are child rape victims among its members, while a source involved in an official investigation says Central American authorities have sworn statements from ex-members that rapes were committed.

"Helbrans cast himself as a Messiah-like figure who could do what he liked because he was a holy man," says Yisrael. "He told us he had come from Heaven to 'mend' people and had supernatural powers and his followers believed him."

One of the ways the group exerts control over its members, Yisrael says, is to remove children from their parents and place them with new "families".

Biological parents are forbidden to have any further contact with them.

This is what happened to Yisrael. At the age of 12, he was taken from their home in Israel, along with his six siblings, to join the group in Guatemala City by their father, Shaul.

Yisrael says Lev Tahor had falsely promised his family that life in Guatemala would be paradise, with animals for the children to play with.

Instead "it was a complete shock," he says. "Everyone was separated from each other. Children had to sleep on stone floors.

We were woken up about 3am every day, then prayers all day long, no food, no water, no talking to other children.

If the rabbi [Helbrans] lectured us, it would go on for hours. Sometimes I would fall asleep standing up.

"Every single thing was controlled. You could only go to the toilet when they said you could."

"We had no education. We did not even study Torah [holiest books of the Jewish Bible] or Talmud [a principal Jewish book of laws] because that would have opened our minds - just Helbrans' writings, which we had to learn by heart. We did not go to sleep until 11pm."

Yisrael says members were only allowed to eat certain vegetables and fruit.

The leaders banned meat, fish and eggs, claiming that they may be affected by genetic engineering.

This they said rendered them unkosher (prohibited under Jewish dietary laws).

Yisrael believes the real reason was just to keep members weak by depriving them of protein.

"Helbrans, though, ate everything he wanted - eggs, fish, meat. He said it was for his health, and you weren't allowed to question it."

Helbrans died in Mexico in 2017, drowning in a river. His son, Nachman, described in US court documents as "more extreme" than his father, took over.

"When I was taken there as a child, I just knew it all felt wrong but couldn't do anything," says Yisrael. "But later I just knew I had to get out."

That point came when his wife Malke had a baby boy, Nevo, two years after they were married.

"They knew where you were at all times, but one day the leaders sent me to get something printed in the town [Oratorio, to where the group had moved]. It was an internet store, and I remembered what a computer looked like from when I was a child back home. I didn't know how to use one, so I asked the store owner for help."

After learning about Google, Yisrael asked the owner to look up Lev Tahor - and was shocked by what he found.

"There were articles about this cult, and it confirmed what I thought." Among the results were reports about how his aunt, Orit, back in Israel, was fighting the group.

"I thought that Orit had forgotten us," says Yisrael. "I didn't know she was doing everything to rescue our family."

Yisrael found her email address and sent her a message. Orit says she was shocked to get it.

They started communicating, with Yisrael returning to the store whenever he was sent on errands. Then using money he had secretly earned, Yisrael bought a mobile phone and rang his aunt.

"When she heard my voice she was so happy," he says with a smile. "She told me she would come to take me out, and a few days after that I escaped."

"One night I slipped out the gate and ran for 15 minutes through the jungle until I came to a highway. I stopped a bus and it took me to Guatemala City, about two hours away. I was frightened members would come looking for me.

"Orit was waiting for me but I didn't recognise her, and at first I didn't know whether to hug her because she was not dressed like women in Lev Tahor, where touching the opposite sex [outside of marriage] was strictly forbidden."

One of the hallmarks of the group is its requirement for females from the age of three to wear a full-body cloak, which it argues is for modesty.

In public, females are seen to also cover their faces apart from their eyes. The practice has earned Lev Tahor the nickname the Jewish Taliban in media reports.

At first Yisrael did not want to leave without his son, but Orit promised they would return for the boy, and they left Guatemala for Israel.

By then 19, Yisrael had in effect been living an isolated existence for five years and struggled to adjust.

"I had to start life from zero," he says, "to meet people, to make friends, to even learn the language again - it was very, very difficult."

He and Orit returned to Guatemala several times to try to reclaim Yisrael's son, but to no avail.

Then, last September, following an undercover operation by a four-man team (including former Mossad agents, an ex-police officer and a lawyer) from Israel, an elite police unit raided Lev Tahor's hideout in Mexico's Chiapas state, to where some of the group had relocated.

The raid had been authorised by a state judge who had examined evidence of criminal activity, including drug trafficking and rape, gathered by Mexico's Special Prosecutor for Organised Crime.

This included an order which the BBC has seen from a leader of the group, instructing mothers to kill their children - apparently with poison - if welfare services came to take them away.

"If some people come to take our children from us… we have to sacrifice lives so the cursed ones will not desecrate the spirit of our pure children… [in] the way it was instructed by our holiness [Shlomo Helbrans] before he died," a translation of the document reads.

"It must be done in a way they [the children] don't suffer… nor disfigure their body… so they [women] will use what we will distribute [which] has to be given to the children immediately… without explaining to them what it is so as not to frighten them."

It then instructs the women to kill themselves after they have killed the children.

Children were immediately separated from adults as a precaution and the compound emptied.

Nevo was among those brought out and was reunited with Yisrael. "I cried," Yisrael says, "but Nevo was calm. I'm sure he felt that I was his father."

Malke was also evacuated but refused to leave the group. She and two dozen others were held at a government shelter, but five days later they escaped.

Two leaders arrested on the orders of the state judge on suspicion of human trafficking and serious sexual offences were freed by a local judge.

Yisrael's account of abuses by Lev Tahor has not been independently verified, but it parallels testimonies of other former members.

A spokesman for Lev Tahor, Uriel Goldman, rejected the allegations.

"I completely deny all the accusations," he told the BBC. "The greatest evidence we have is the words of the [local] judge in Mexico. After hearing all the evidence from A to Z, the judge decisively decided to close the case." Mr Goldman said the group was the victim of "a persecution".

Although the finding by the local judge has not been set aside, a source with intimate knowledge of the case says they were not presented with the evidence gathered by the federal investigator.

All those who fled from the government shelter in Mexico, as well as the two freed leaders, have returned to Guatemala, according to the source.

Some 8,000 miles (12,000 km) away, Yisrael continues to rebuild his life with Nevo at their new home on the outskirts of Tel Aviv.

Forbidden from using technology for years, he is now studying computer science at Bar Ilan University, with the aim of becoming a software engineer.

"After that," he says, "the sky's the limit."