manila philippine troop friday rescue three vietnamese sailors abduct group islamist militants nine months ago dangerous southern water near malaysian border army spokeswoman say seventeen vietnamese sailors take captive south philippines pro-islamic state militants attack commercial ship sulu celebes seas generate millions dollars ransom payments four vietnamese sailors find remote island tawi-tawi one already dead illness captain jo-ann petinglay tell reporters say philippines marines pursue small group militants flee abandon captives 17 vietnamese sailors abduct february 10 rescue early operations two kill militants attempt escape say rest bring nearby jolo island add without elaborate military say militants know kidnap bomb behead captives still hold 16 captives jolo island include seven foreigners include dutch japanese national philippine troop rescue three vietnamese islamist militants