seoul north korea may conduct additional missile test year polish long-range missile technology ramp threat unite state south korea spy agency say monday add monitor developments closely north korea pursue nuclear weapons missile program defiance u.n. security council sanction make secret plan develop missile capable hit u.s. mainland fire two missiles japan reclusive state appear carry recent missile engine test brisk movements vehicles spot near know missile facilities yi wan-young member south korea parliamentary intelligence committee brief seoul national intelligence service say sign imminent nuclear test detect yi note third tunnel punggye-ri complex remain ready another detonation time construction recently resume fourth tunnel make use time agency closely follow developments possibility north korea could fire array ballistic missiles year name satellite launch peaceful development space fact ratchet threats unite state lawmakers tell reporters closed-door brief spy agency north korea defend weapons program necessary defense u.s. plan invade unite state 28,500 troop south korea legacy 1950-53 korean war deny intention pyongyang also carry sweep ideological scrutiny political unit military first time 20 years accord kim byung-kee another lawmaker committee probe lead rule workers party organisation guidance department orchestrate choe ryong hae head general political bureau korean people army replace hwang pyong may 2014. result hwang kim hong seoul unification ministry say remove office mid-january minister stasi-like secret police call bowibu punish lawmaker say elaborate choe subject political reeducation past appear gain influence since promote october party powerful central military commission national intelligence service indicate choe head organisation guidance department secretive body oversee appointments within north korea leadership choe command organisation guidance department undertake inspection military politburo first time 20 years take issue impure attitude toward party leadership lawmaker kim say separately monday south korea approve request south korean attend event north mark anniversary death mother formerly lead chondoist chongu party minor north korean political party son identify surname choi first south korean visit north since liberal president moon jae-in take office may schedule arrive pyongyang via china wednesday return saturday accord seoul unification ministry senior chinese official wrap four-day visit north korea monday apparently without meet country leader kim jong un song tao head international department chinese communist party meet senior officials workers party korea exchange view korean peninsula issue china official xinhua news agency say rule party china democratic people republic korea monday pledge strengthen inter-party exchange coordination push forward relations add use north korea official name song pyongyang discuss outcome recently conclude chinese communist party congress beijing south korea fear missile advance north year threat u.s