A homemade bomb ripped through a bus and wounded six passengers in the southern Philippines in an attack blamed on an extortion gang led by former Muslim rebels, police said. Koronadal city police chief Froilan Quedilla said the device, made from a mortar shell, exploded as the bus was about to enter a terminal Saturday. It was the fourth attack in three weeks on the same bus company, which has ignored extortion attempts by the Al-Khobar group, and came several days after a suspected gang member was arrested. Al-Khobar is suspected of carrying out bombings when extortion or ransom payments are not made. It was allegedly behind several deadly bombings of buses and business establishments that occurred since 2007.