seoul u.s. south korean defense chiefs agree deploy u.s. missile defense system south korea year counter threat north korea south korea defense ministry say friday u.s. defense secretary jim mattis two-day visit seoul meet south korean top officials include defense minister han min-koo two agree deploy operate terminal high altitude area defense thaad system within year plan defense system solely north korea missile threat south korean defense ministry say statement refer meet han mattis u.s. south korea agree deploy thaad year south say