(CNN) -- Police in Pakistan raided an Islamic religious school Monday and found 50 students chained to one another and being held in an underground room.
Video footage from the madrassa showed young men and boys -- some appearing to be as young as 8 years old -- with heavy chains connected to their ankles.
According to details reported by CNN affiliate GEO news, police conducted the raid at the Islamic school in Sohrab Goth -- a suburb of Gadap in Karachi -- after sources told Gadap police officers of children kept in an underground dungeon.
Police said the students reported they were beaten and shocked with electric wires.
It was not immediately clear why the students were being kept in such conditions, or how long they had been there. The school's imam was taken into custody for questioning, police said.
Speaking to GEO news, Gadap police official Rao Anwar said the majority of the children were from the Khyber Pakhtunkhwa region of North West Pakistan.
The students were enrolled in the madrassa by their parents to be religiously trained. Police said parents were unaware of the conditions their children were kept in.