Transcript for Tensions mount between the US and North Korea

We now want to turn our other top story, the growing showdown between the U.S. And North Korea. President trump and Kim Jong-un trading threats of military action. After the president warnd that the U.S. Was locked and loaded, North Korea responded with a threat of its own, promising tragic doom to America. Here's ABC's Martha Raddatz. Reporter: Today, a new warning from Kim Jong-un's regime. After nearly a week of threats on both sides, north Korean state media sending this message. "If the trump administration does not want the American empire to meet its tragic doom, they had better talk and act properly." The threat comes after North Korea, earlier this week, said it was crafting a plan to send four missiles to the waters off Guam. And its latest message, clearly a response to president trump's string of warnings, from his Friday tweet, saying the U.S military is "Locked and loaded" to his latest. And if anything happens to Guam, there's going to be big, big trouble in North Korea. Reporter: The governor of Guam, urging calm to the 160,000 Americans who live there. Today, he received a call from the president. We are with you 1,000%. Reporter: The president even promising him a tourism boom. Jouf become extremely famous. Your tourism -- you're going to go up like tenfold with the expenditure of no money, so I congratulate you. Reporter: Still, U.S. Officials tell ABC news there is no high alert for U.S. Forces here. They are always in a state of preparedness. But should conflict break out, it's the citizens here of south Korea who could pay the steepest price. There are also 14,000 tubes of artillery which could rain down on South Korea's capital of Seoul if they intended to do that with over 26 million people caught in the crosshairs. The north, so reclusive, that these leaflets with messages are launched into North Korea from the south. Lee min-bok says he defected to the south after reading one. And now delivers his own. Translator: After reading the leaflet I just knew that the north regime was all false. So I decided to flee to the south. What do you think it's like for the people who are still in the north today? Translator: I just have to say one word -- it is slavery, mentally and physically. What you can see from this observation point is really just propaganda. Across the river, North Korea, you can see some apartment buildings, some other structures, but if you look through those observation glasses, you can see they are all fake. Reporter: Crucial to solving this crisis, China, north Korea's biggest trading partner. China urging restraint from both sides in a phone call between president trump and president XI late last night. The world is used to fiery rhetoric from North Korea but not from a U.S. President. Made all the more serious this time because intelligence analysts believe that the north can now arm an icbm with a nuclear war head.

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