The bombing happened as a prominent religious scholar during a special class was delivering a lecture about the teachings of Islam at the main hall of the Jamia Zubairia madrassa, said police officer Waqar Azim. He said initial investigations suggest the bomb went off minutes after someone left a bag at the madrassa.
TV footage showed the damaged main hall of the seminary, where the bombing took place. The hall was littered with broken glass and its carpet was stained with blood. Police said at least 5 kilograms (11 pounds) of explosives were used in the attack.
Several of the wounded students were in critical condition, and hospital authorities feared the death toll could climb further. Authorities said some seminary teachers and employees were also wounded in the bombing.