Trump to North Korea: Be very, very nervous
Mr Trump meanwhile denied there were any mixed messages from his administration.
Earlier this week, US Secretary of State Rex Tillerson played down the rhetoric between the two sides.Media playback is unsupported on your device
But in an interview with the BBC on Thursday, White House Deputy Assistant Sebastian Gorka dismissed the top diplomat's comments.
"You should listen to the president," he said. "The idea that Secretary Tillerson is going to discuss military matters is simply nonsensical.
Mr Gorka recalled a quote from a Holocaust survivor he often refers to when lecturing on grand strategy, saying: "When a group of people repeatedly says they want to kill you, sooner or later you should take them seriously".
"North Korea has said they wish to annihilate the United States and use nuclear weapons. Sooner or later, somebody should take them seriously," he said.
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