MOSCOW—Russian investigators opened a criminal case into a knife attack at a school in the city of Perm on Monday which left 15 people injured, three of whom the authorities said were in a serious condition in hospital.
Media reports initially said two masked men armed with knives had burst into the school and attacked pupils, but authorities in Perm, about 700 miles north-east of Moscow, said the attack grew out of a knife fight between two pupils.
