The raid in Katsina was the third such operation in less than a month, bringing the total of people freed to around 1,000.
More than 500 boys and young men have been rescued after they were chained to walls, beaten up and sexually assaulted in an Islamic school in northern Nigeria.
The raid in Katsina was the third such operation in less than a month, bringing the total of people freed from abusive conditions to around 1,000.
President Muhammadu Buhari’s government is under pressure to take urgent action to free the potentially thousands of other children who remain in similar schools across Nigeria.
In September, police freed captives of an alleged Islamic school in neighbouring Kaduna state, some of who had been beaten up so badly they needed help walking.
The youngest victims were around five years old, and the oldest were in their late teens. Some had their ankles manacled together, while others were chained by their legs.
Several victims had visible marks on their bodies that showed they had been tortured, police in the city of Kaduna said.
Police declined to comment on the raid and blocked entrance to the grounds.
A police source said that not all of the freed 500 students had been mistreated. One well-kept building held 300 pupils who were allegedly not regularly mistreated.
But 200 captives at a site next door were regularly abused.
The second camp is the dangerous place,” the police source told Reuters. “The children were molested there.”
The source added that the most unruly students and some newcomers were placed in the second building.
Students at the first building were allegedly sometimes taken to the second building for abuse.
Islamic schools, called Almajiris, are common in the mostly Muslim north of Nigeria.
Around 10 million children attend them, according to local organisation Muslim Rights Concern.
Mr Buhari, whose home state is Katsina, said earlier this year that he planned to ban Almajiris, but would not do so right away.
An aide said Mr Buhari had directed police: “Go out in search of these kind of centres wherever they are and disband them.”
The centres referred to the places where people are maltreated in the name of religion, the aide said.