As many as 50 students have been rescued from a religious school in the Pakistani city of Karachi, where they were allegedly tortured.

The boys, some as young as 12, were kept in an underground chamber and say they were beaten and deprived of food.

A police official told the BBC that most of the students were drug addicts who were sent to the school for treatment.

Pakistan's interior minister has ordered an inquiry.

Orla Guerin reports.