KARACHI – Unidentified attackers on Saturday lobbed a hand grenade and opened fire at a primary school in Karachi, killing its principal and wounding eight others, among them five students, police said. Witnesses said a passing out ceremony on the result day of the school was in progress when unidentified men tossed a cracker into the school located in Rehmania nehigbourhood of Baldia Town. All the students aged between five and ten. The gunmen fired at the school gate and fled on their bikes, police said, adding the principal, an Awami National Party member, had refused to bow to militant demand to close down the school. However, no group claimed the responsibility for the attack until the filing of this report. The principal of The Nation School, Abdul Rashid, 40, was pronounced as brought dead by the doctors. Five students, Tahira Nazir, Amna Kareem, Attya Rashid, Madiha and Hina, a teacher Mian Syed, peon Gulshair were under treatment at the hospital, rescuers said. They also said that two of the eight injured students were in critical condition. The incident took place at a time when the staff and the students assembled in the courtyard of the school for examination result announcements. According to police, the bomb could not hurt anyone but the shooting did. According to officials of the Bomb Disposal Squad, the grenade contained 250 grams of explosive material. Police said a case had been registered and investigation was in an advanced stage. The victim, Rashid, had survived an attack in the same area in recent times. He never complained or registered a case with the police. The attack took place in the low-income Ittehad Town neighbourhood of Karachi - a city of 18 million people plagued by murders, kidnappings and politically linked violence.The Taliban recently warned people to stay away from rallies and political activities of ANP, Muttahida Qaumi Movement and Pakistan People’s Party.Baldia Town is located in the western outskirts of the city and is said to be a hotbed for Taliban and other banned outfits.For the past several days police and Rangers have carried many operations and crackdowns and arrested dozens of suspect Taliban and other criminals from the area. A huge quantity of weapons and explosive material were also recovered in the operations.The latest attack follows the murder earlier this week in the Khyber Agency of Shahnaz Nazli, a 41-year-old teacher gunned down in front of one of her children only 200 metres from the all-girls school where she taught. But this time the wave of terror attacks  is provoking a domestic and international response, a groundswell of public revulsion similar to that which followed the attempted assassination of Malala Yousafzai, who was also shot simply for wanting girls to go to school.Last October, shocked by the attempted assassination of Malala Yousafzai and pressured by a petition signed by three million people, the government agreed for the first time to legislate compulsory free education and provided stipends for three million children.