Troops fought separatist Tamil guerrillas in northeastern Sri Lanka and sank a rebel boat off a nearby coast, killing up to 15 rebels, the military said Monday. The fighting started late Sunday night when the Sri Lankan navy found two clusters of boats belonging to the Tamil Tiger rebels moving toward the Pulmoddai area in northeastern Sri Lanka, the military said in a statement. When the naval boats went to investigate, the rebel craft attacked, sparking a three-hour sea battle, the military said. One rebel boat was sunk and several others were seriously damaged, the military said. Naval officials said they believed as many as 12 rebels may have died when the vessel went down.