The Philippine military has sent in extra troops to the volatile island of Jolo in a crackdown against Muslim rebels after the death of at least 26 of its soldiers. It follows some of the heaviest fighting in nearly three years between government troops and the separatists, most of whom belong to Abu Sayyaf, part of the regional Islamic militant network Jemaah Islamiyah. More moderate separatists are also thought to be involved. Fighting has so far been confined to a small part of the island but there are fears it could spill over to nearby areas and that other rebel groups could take advantage of the situation. The islands in the southern Philippines are hotbeds of extremism, and are also home to pirate gangs that prey on shipping in the South China Sea.