Transcript for North Korea responds to Trump's promise to unleash 'fire and fury' against any new threat

Good evening, and it's great to have you with us here on a Wednesday night, and we do begin with breaking news. That headline, North Korea just a short time ago, issuing its newest threat. The ap now reporting that the north Korean regime is calling president trump's words a load of nonsense, saying they will complete their plan to, quote, attack waters near Guam by mid August. It comes after president trump warned North Korea against making any more threats or the U.S. Would unleash fire and fury unlike anything the world has ever seen. ABC's senior white house correspondent, Cecilia Vega, leading us off. Reporter: Tonight, a new threat from North Korea coming in, saying they will be ready to attack the U.S. Territory of Guam by mid August. This comes as president trump's shots fired at Pyongyang sent shock waves around the world. But ABC news has learned that threat caught some in the president's own inner circle by surprise. The president, in that statement, using language not vetted or pre-approved by his national security team. North Korea best not make any more threats to the United States. They will be met with fire and fury like the world has never seen. Reporter: Sources close to the president say behind closed doors with top aides -- including new chief of staff general John Kelly -- he had discussed taking a tougher tone on Pyongyang. But even members of his own national security team had no idea the president would go this far. He has been very threatening beyond a Normal statement and as I said, they will be met with fire, fury and frankly power the likes of which this world has never seen before. Thank you. Reporter: Within a few hours, North Korea responding with its own warning. Saying it is "Seriously considering" a plan to target Guam with missiles. The U.S. Territory -- home to crucial military bases and 160,000 Americans -- is just 2,000 miles away. Then today, Rex tillerson sending a message of his own, landing in Guam, offering very different words. I think Americans should sleep well at night. Reporter: The secretary of state striking a much softer tone. What the president is doing is send a strong message to North Korea in language that Kim Jong-un would understand because he doesn't seem to understand diplomatic language. Reporter: Then, the president himself weighed in, tweeting -- our nuclear arsenal is "Now far stronger and more powerful than ever before. Hopefully we will never have to use this power." But his initial words have sparked international reaction. From New Zealand. I think the comments are not helpful in an environment that is very tense. Reporter: To Germany's foreign office saying, saber-rattling won't help. Even some in the president's own party calling his words dangerous. All it's going to do is bring us closer to some kind of serious confrontation. I think this is very, very, very serious. The great leaders that I've seen, they don't threaten until they're ready to act. And I'm not sure president trump is ready to act. And Cecilia Vega is with us live tonight from bedminster, New Jersey, where the president is vacationing at his golf course. You have more on the north Koreans at this hour, and any response from the white house tonight? Reporter: No response from the white house because this statement literally just came in. I want to read a bit of it. It's from a top army commander given out by state media. They say this is a crucial warning to the United States calling a fire and fury by president a load of nonsense. They say this has infiuriated the army, and they say this plan will be complete by mid August, David. Cecilia Vega who will be covering this into the night. Cecilia, thank you. ABC's chief global affairs correspondent, Martha Raddatz with us on this breaking development. This threat from North Korea, and you have been talking to your sources at the Pentagon. A lot of Americans watching want to know how unlikely is it. Will we see military conflict here? Reporter: President trump's statement was a surprise to many. It is important to say war is the last thing anyone at the Pentagon wants to see happen, but pacific command has been doing updated war planning and they are certainly focusing on defensive measures as well, but if those tough sanctions imposed on North Korea do not work, if Kim Jong-un continues to make progress on a nuclear tipped missile, a senior official told me in 6 to 12 months, the administration will have to decide whether some sort of pre-emptive strike or some other measure should be undertaken to stop Kim, David. Martha Raddatz following the breaking developments as well. Thank you.

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