seoul decorate pyongyang blacklist abroad two scientists picture north korea leader ahead sunday nuclear test play vital roles reclusive country pursuit powerful weapon capable strike unite state experts say north korea sixth nuclear test sunday show country either develop hydrogen bomb vastly destructive power atomic bomb get close obtain one photos release official kcna news agency hours test show two men stand alongside leader kim jong un inspect new peanut-shaped warhead ri hong sop head north korea nuclear weapons institute hong sing mu deputy director rule workers party korea munition industry department several north korea leadership experts say part cadre weapons experts frontline young leader state ambition develop intercontinental ballistic missile icbm carry nuclear weapon unite state compare father kim jong il grandfather kim il sing prefer small work group middle managers deal weapons program 33-year-old leader personally involve scientists experts say cite frequent appearances technocrats state events weapons test field inspections appear hong spearhead nuclear development program senior party official ri charge nuclear test hydrogen bomb work level say yang moo-jin professor university north korean study seoul monitor country hierarchy leadership reuters could independently confirm precise role two men north korean government provide foreign media contact point pyongyang comment email fax phone north korean mission unite nations immediately available comment two scientists become increasingly high profile pyongyang weapons program advance rapid pace kim leadership reuters review north korean state media show january 2016 hong ri first second line receive medals personally award kim ceremony mark country fourth nuclear test state tv footage show two months late accompany smile kim inspect silver-colored sphere north say miniaturize warhead capable fit icbm wide group weapons technocrats include trio rocket scientists accompany kim several crucial missile launch include two july icbm test launch show much u.s. mainland within range experts say kim hands-on approach may contribute fast development nuclear weapons missiles allow scientists develop personal link leader kim jong un go way show personal closeness say michael madden expert north korean leadership point kim frequent appearances cadres engage weapons program likely link fact scientists make huge accomplishments area thus make big accomplishments kim jong un leader north korea like three rocket scientists ri hong blacklist recent years unite nations unite state south korea roles north korea weapons program unite nations blacklist ri 2009 cite involvement production weapons-grade plutonium expert un panel year note hong key role country nuclear program recommend also sanction ri former director yongbyon nuclear research centre north korea main nuclear facility north pyongyang yongbyon operate country first nuclear reactors confirm uranium enrichment facility siegfried hecker nuclear science professor stanford university one last americans visit yongbyon recall meet ri several visit 2004 2008. one visit ri show hecker around plutonium reactor radiochemical lab ri state pride north korea nuclear researchers master plutonium production outside help hecker say 2006 report yongbyon visit standford center international security cooperation hecker immediately respond request comment ri north korean nuclear program statement carry kcna hours sixth test kim say components hydrogen bomb homemade allow north korea produce nuclear weapons many want hong former chief engineer yongbyon rule party munition department since mid-2000s rise prominence kim jong un take power december 2011 follow death father accord south korean government database hong 75 see accompany kim nuclear test long-range missile launch since 2012 south korean database picture release kcna show educate central eastern europe possibly russia well ri attend seminars abroad north korea leadership expert madden say top-level officials last generation study old communist world good old days say north korea 's nuclear scientists take center stage h-bomb test