Nearly 500 young boys and men have been rescued from a "torture house" where they were chained up, abused and forced into slavery, say police.
Some of the boys and men had been held captive for years inside the building of horrors, which was advertised as an Islamic school, in Kaduna, Nigeria.
Victims as young as five had been tortured, sexually abused and starved while they were prevented from escaping, according to police, and there were signs they were being indoctrinated.
Many of the children had metal chains around their ankles and visible injuries, and one of those who saved claimed detainees had died.
Police said eight people have been arrested and all of them were said to be teachers.
Some of the children told police they were taken to the building by relatives who thought it was a Koranic school.
Bello Hamza, who spent three months in chains, told reporters: “I got admission to study applied mathematics, but here I am chained.
"They claim to be teaching us the Koran and Islam but they do a lot of things here. They subject the younger ones to homosexuality."
There is no evidence to suggest the building was ever a school, according to police.
Bello, 42, claimed: “This is supposed to be an Islamic centre, but trying to run away from here attracts severe punishment; they tie people and hang them to the ceiling for that, but engaging in homosexuality attracts no punishment.
"Within my short stay here, somebody had died as a result of torture.
"Others have died before my coming due to poor health and torture.
"They give us very poor food and we only eat twice a day; 11 am and 10 pm.
“They have denied me a lot of things here. I am a family man, I have responsibilities, but I am chained here not knowing what is happening to my family members.”
Some of those who were being held captive and tortured were from outside Nigeria, including Burkina Faso and Mali.
Police chief Ali Janga told the BBC the large house was raided following a tip-off about suspicious activity.
He described it as a "house of torture" and said it was a case involving human slavery.
He told reporters: “We received information that something is going on in this rehabilitation centre or Islamic centre.
"On getting here, we discovered that this is neither a rehabilitation centre or Islamic school.
“These people are being used, dehumanised."
Police said there were signs that the victims were being indoctrinated, according to Sahara Reporters, which published Bello's interview.
According to that report, the owner of the building said: “Those chained are the stubborn ones who attempted to run away. Those who don’t attempt running away are not chained.
"Some were chained before and after settling down, they were freed.
“Most of them were brought by their parents from across the country and others from outside the countries
“All those allegations of torture, dehumanisation, and homosexuality are false. We do nothing here other than teaching people Islam.
“They don’t do anything other than, recitation of Koran, pray and worship God."
The police chief said the victims were overjoyed to finally be free after months or years in captivity.
After their rescue they were taken to a stadium to be cared for until their families could be notified.
Yakubu Sabo, the Kaduna police spokesman, told Reuters: "The state government is currently providing food to the children who are between the ages of five and above."
Islamic schools, known as Almajiris, are common across the mostly Muslim north of Nigeria - a country which is roughly evenly split between followers of Christianity and Islam.
