washington unite state press china exert economic diplomatic pressure north korea help rein nuclear missile program round high-level talk washington wednesday meet top u.s. chinese diplomats defense chiefs hold day president donald trump say china efforts use leverage pyongyang fail raise fresh doubt administration strategy counter threat north korea death american university student otto warmbier week release 17 months imprisonment pyongyang complicate trump approach north korea top national security challenge reiterate china diplomatic responsibility exert much great economic diplomatic pressure regime want prevent escalation region u.s. secretary state rex tillerson tell reporters joint news conference defense secretary jim mattis mattis vow continue take necessary measure defend ally north korea work develop nuclear-tipped missile capable hit unite state long-standing option pre-emptive military strike see far risky trump aid stress economic diplomatic pressure tillerson say trump would make state visit china year mattis say side agree expand military-to-military tie signal new administration determination continue efforts improve relations world two large economies despite frustration north korea north korea top agenda newly establish diplomatic security dialogue pair tillerson mattis chinese state councilor yang jiechi general fang fenghui chief joint staff people liberation army u.s. officials stress agreement goal north korean denuclearization talk also deal china sweep territorial claim south china sea americans reaffirm opposition beijing militarization islands build strategic waterway tillerson urge china help crack illicit north korean activities fund nuclear missile program say chinese agree company business sanction north korean entities tillerson stress need choke fund source include money launder labor export computer hack countries around world u.n. security council join effort hope china part well say china north korea main trade partner accuse fully enforce exist u.n. sanction neighbor resist tough measure washington consider secondary sanction chinese bank firm business north korea chinese foreign ministry spokesman say china exert so-called economic diplomatic pressure interactions countries develop friendly cooperative relations basis five principles peaceful coexistence spokesman geng shuang tell regular brief thursday trump high hop cooperation china exert influence north korea lean heavily chinese president xi jinping assistance two leaders meet florida april trump praise xi work issue despite modest step far beijing time trump mostly hold back attack chinese trade practice rail presidential campaign greatly appreciate efforts president xi china help north korea work least know china try trump write twitter tuesday day warmbier die follow return captivity coma tweet puzzle even trump aid ask whether trump lose faith china ability restrain north korea mattis say president view represent americans frustration pyongyang provocations see young man go healthy minor act mischief come home dead basically late wednesday trump say speech cedar rapids iowa unite state great relationship china really like president xi talk follow u.s. official say tuesday new movements detect u.s. spy satellite north korea nuclear test site unclear pyongyang prepare sixth nuclear test high-level talk u.s. ask china rein north korea