At least 300 students, many in chains, rescued from a building housing an Islamic school in Kaduna city, say police.
At least 300 captives, most of them children and many in chains, have been rescued from a building in the northern Nigerian city of Kaduna, a spokesman for the police said.
Yakubu Sano told reporters on Friday that police raided the building, which housed an Islamic school in the Rigasa area, and found adults and minors in "the most debasing and inhumane conditions".
"We found around 100 students, including children as young as nine, in chains stuffed in a small room, all in the name of reforming them and making them responsible persons," he said.
It was not clear how long the children had been held at the building.
Two of them were from Burkina Faso while most of the rest were from northern Nigerian states, according to the police.
During Thursday's raid on the school, police said they found a "torture chamber" where students were chained, hung and beaten. Many of the rescued students bore scars on their backs and serious injuries.
"The victims were abused. Some of them said they were sodomised by their teachers," Sano said, adding that seven teachers at the school have been arrested.
One inmate quoted by Nigerian media described horrific conditions and treatment at the facility.
"I have spent three months here with chains on my legs," Bello Hamza said, adding that he was meant to be in South Africa studying for his master's degree.
"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."