Transcript for Trump issues new warning for North Korea

First the latest on those rising tensions with North Korea. President trump as you heard doubling down on his warning to Kim Jong-un and his regime saying maybe he wasn't tough enough. You know meanwhile, 167,000 Americans are in Guam and they're being told what to do in the event of an attack. After that warning from Kim Jong-un. We have team coverage across the globe from South Korea to Washington and Martha Raddatz starts us off from Seoul just 50 miles from the north Korean border. Good morning, Martha. Reporter: Good morning, George. There is uncertainty and tension here on the Korean peninsula. People just don't know what's going to happen next and president trump is doing nothing to tamp down the fear. This morning, tensions escalating. President trump with that newest dire warning for north Korean leader Kim Jong-un after his threat against Guam. Let's see what he does with Guam. He does something in Guam, it will be an event the likes of which nobody has seen before what will happen in North Korea. He will see. Is that a dare? Is that a dare? It's a statement. Has nothing to do with dare. That's a statement. Reporter: The president firing back after North Korea in a statement Tuesday called the president senile and his commencomme comments nonsense. It's the first time they heard it like they heard it, and, frankly, the people that were questioning that statement, maybe it wasn't tough enough. They've been doing this to our country for a long time, many years and it's about time somebody stuck up for our country and the people of other countries. Reporter: Not saying whether a preemptive trike is being considered. We never talk about that. Reporter: Overnight James Mattis stressing the efforts to reach a peaceful resolution. You can see the American effort to diplomatically led. It has diplomatic traction. It is gaining diplomatic results. The tragedy of war is well enough known it would be catastrophic. Reporter: President trump also leaving the door open for negotiations. Sure, we'll always consider negotiations. Reporter: The president's latest comments coming after North Korea said it would launch four missiles at waters near Guam by mid-august. And despite those threats from North Korea to lob missiles at Guam, officials tell ABC news there is no evidence that any missile launch is imminent. George. And not on any more of a war footing. Thanks very much.

This transcript has been automatically generated and may not be 100% accurate.