Transcript for Kim Jong Un reacts to Trump's UN speech

Tensions escalating with North Korea in the wake of president trump's U.N. Address and new executive order increasing sanctions. Kim Jong-un calling president trump, quote, mentally deranged and now North Korea is threatening to test a hydrogen bomb over the pacific ocean. Cecilia Vega live in Washington with the latest for us. Good morning, Cecilia. Reporter: David, good morning to you. Just a few minutes ago president trump firing right back at north Korea. This time on Twitter. Take a look at what he wrote. Kim Jong-un of North Korea who is obviously a madman who doesn't mind starving or killing his people will be tested like never before. This is an escalation in this war of words and neither side is backing down. North Korea's leader this morning has a message for president trump. Kim Jong-un saying in a statement, now that trump has denied the existence of and insulted me and my country in front of the eyes of the world and made the most ferocious declaration of a war in history we will consider a corresponding highest level of hard-line countermeasure in history. And overnight his foreign minister said that highest level could include testing a hydrogen bomb over the pacific ocean. It is a direct response to the president's fiery address at the united nations. The United States has great strength and patience, but if it is forced to defend itself or its allies, we will have no choice but to totally destroy North Korea. Reporter: Now Kim Jong-un says president trump will pay dearly for those words. Vowing whatever trump might have expected, he will face results beyond his expectation. Calling him mentally deranged, a gangster unfit for office. This as the president put aside the talk of war on his final day at the U.N., instead announcing another round of economic sanctions. It is unacceptable that others financially support this criminal, rogue regime. Reporter: With the leaders of South Korea and Japan right by his side, the president said China, North Korea's largest trading partner, has agreed to take tough, new steps to isolate Kim Jong-un. China's biggest banks immediately ending business with Pyongyang. Now, one line in particular from Kim Jong-un's stajt really caught the attention of Americans. He said I will surely and definitely tame the mentally deranged U.S. Dotard with fire. Searches for the meaning of that word spiked overnight. It means an old person especially one who has become weak or seen nile and, robin, it is now trending online. Many had to look up that word. New developments in the

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