The school owner told police he was running an Islamic school to reform the students, according to the police spokesman. However, police said there is no evidence the school was actually being used as a religious facility.

The group of men and boys, some as young as 13, were freed after police learned children were being held in chains at a school in the northern city of Kaduna, Sabo said. Kaduna is 150 kilometers (about 93 miles) north of Nigeria's capital, Abuja.

Six teachers and the school owner were detained and questioned by police. CNN called the school seeking comment but nobody answered the phone.

Sabo said some of the men were chained and hoarded in a very confined space, adding that the men "were not hostile" and "there is no reason why they should have been held in such a place."

Some of the detainees, especially children, had scars on their bodies and told the police they had been sexually abused in the school, according to the spokesman.

"They had scars and some marks of torture and violence on them. They were pleading they should be taken out of the place and they have been evacuated from that facility," Sabo said.

Police are working with state authorities to reunite the men and boys with their families.

Some of the detainees, who were from neighboring countries, including Burkina Faso and Mali, said they were brought to the school by their parents. CNN