washington chairman u.s. senate east asia subcommittee ask china 20 nations monday clamp north korea cut tie close diplomatic facilities work oust country unite nations north korea defy u.n. security resolutions conduct nuclear ballistic missile test washington scramble effective response many president donald trump fellow republicans call tough action impose quickly include call stiff secondary sanction punishments company bank countries business north korea letter see reuters send ambassadors china 20 countries republican senator cory gardner subcommittee chairman ask countries immediately end diplomatic economic relations pyongyang maintain official diplomatic relations regime continue defy international law threaten nations across globe serve reward nefarious behavior write gardner addition cut bilateral tie urge government support expel dprk unite nations letter say gardner recently introduce legislation would impose u.s. economic embargo entity business north korea u.s. military stag bomb drill south korea korean peninsula russia china begin naval exercise ahead u.n. general assembly meet tuesday north korea nuclear threat likely loom large gardner letter send ambassadors unite state china brazil britain bulgaria cambodia cuba czech republic egypt germany india indonesia laos malaysia mongolia nigeria pakistan poland romania russia sweden vietnam u.s. lawmaker want north korea u.n