As many as 50 students have been rescued from a madrassa (religious school) in Karachi. Pakistani officials say some were being kept in chains.
The students, some as young as 12, were reportedly beaten, deprived of food and kept in what police say was a torture chamber.
The BBC reports some parents had paid for their children to attend Madrassa Zakarya because their sons were addicted to drugs or involved in crime.
They were chained to prevent them from escaping. Correspondents say that in some cases parents actually applied the chains which imprisoned their children.
Police raided the premises late on Monday. At least two people helping run the madrassa were arrested, but police say the head escaped.
Some schools in Pakistan are accused of being training camps for Islamic groups, but while police say the primary reason there students were there was for rehabilitation.