washington u.s. secretary state rex tillerson believe diplomatic tiff russia unite state escalate hop two countries begin work improve tie state department spokeswoman say tuesday think secretary believe escalatory action necessary point look forward try forge ahead state department spokeswoman heather nauert tell brief ask possibility diplomatic cut two side nauert also note ambassador joseph yun u.s. special representative north korean policy moscow tuesday talk russian officials efforts curb pyongyang nuclear missile program u.s. diplomatic tiff russia escalate state department