A bomb exploded inside an Islamic school in southwestern Pakistan on Monday, killing six people and wounding four others, officials said. The explosion ripped through the madrassa in Qilla Saifullah, a town about 140 kilometers (87 miles) north of Quetta, the capital of Baluchistan province, police official Mohammed Farooq said. The bomb exploded in a room soon after an Afghan refugee, who stayed there for the night as a guest, had left, Farooq said. Four school students were killed at the scene while two others died later. Four more people were wounded, Farooq said.