Transcript for Tensions escalate between Trump and Kim Jong Un

Next up, the U.S. With a show of force, sending a message to North Korea. American bombers flying near the north Korean coast. As president trump and the regime trade new insults. The president calling Kim Jong-un little rocket man. North Korea warning that an attack on the U.S. Is becoming more inevitable. Here's Bob woodruff. Reporter: American b-1 bombers and f-15 fighter jets took off in the night, flying farther north of the dmz than any time in nearly two decades. While in Pyongyang this weekend, thousands marched through the streets during a rally against the U.S. The show of force from both nations comes as the volley of insults reaches an alarming level. President trump tweeted Saturday, "Just heard foreign minister of North Korea speak at U.N. If he echoes thoughts of little rocket man they won't be around much longer." His tweet comes after the north Korean foreign minister slammed the president at the united nations, calling him "A mentally deranged person" who "Committed an irreversible mistake." Days earlier, president trump in the same venue with that warning. If it is forced to defend itself or its allies, we will have no choice but to totally destroy North Korea. Reporter: North Korea then threatened to test a hydrogen bomb above the pacific ocean, something they have never done before. Everything he has said he would do. I will test a hydrogen bomb, I will send an icbm test. He's done. So why wouldn't he test a hydrogen bomb over the pacific? I think the likelihood is there that he will test a bomb at some point. And Bob joins us live. You've been covering North Korea for more than a decade, you were just on the north korean/china border. And you told me something you've never seen before? The tension is growing. Probably with more missile launches and nuclear tests. But bottom line, they have no idea what Kim Jong-un will do, he's unpredictable compared to his father and grandfather.

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