As we come on the air, one of the most dangerous countries in the world today is making a new threat directly aimed at the united states. North korea, the secretive nation, with its mysterious young... See More
As we come on the air, one of the most dangerous countries in the world today is making a new threat directly aimed at the united states. North korea, the secretive nation, with its mysterious young dictator, announcing they will test their nuclear powers and saying they will put america on notice. Let's bring in our chief global affairs correspondent martha raddatz right now to tell us how serious this new aggression is. Martha? Reporter: Diane, the u.S. Is warning north korea not to try another nuclear test, saying it would be a mistake and needlessly provocative. But those warnings seem only to have provoked the new, young leader even more. If there was any hope that kim jong-un would be less threatening and dangerous than his late father, those hopes are now dashed. The 20-something leader appears to relish his new role, now directly challenging the united states. The reclusive nation warning the world that it will soon test a nuclear weapon, long range rockets, one after another. Today, vowing that the target of its missiles and nuclear aggression, america. Their sworn enemy. He's trying to show he can't be pushed around. Reporter: Tonight, deep inside the isolated nation, there are signs that a nuclear test is being readied. North korea first tested a nuclear bomb in 2006. Diane sawyer was inside north korea days after that test, the only western journalist meeting with the north's nuclear negotiators, who asserted their country's right to test. Now, it's believed the secretive regime has a nuclear arsenal of as many as 12 weapons. And powerful ones. Their last test in 2009 revealed a bomb about half as powerful of the one that destroyed hiroshima. Models show such a bomb could level an area roughly about the size of, say, lower manhattan. So, how big a threat is north korea? It's believed their missiles can travel about 6,000 miles at best, but capable of hitting hawaii. But what they are lacking, and this is critical, is the ability to make a nuclear weapon small enough to be placed atop a missile and launched at an enemy. It's believed north korea is still many years away from being able to do that. Still, as today shows, a nation which proudly hangs anti-american posters, such as this, while struggling to feed its own people, is working every day to become an even greater threat. This is one of the very serious challenges that the next secretary of state will have to face. And quince dentally, the nominee for that job, senator john kerry, was on capitol hill today for his confirmation hearings, as you know, diane. That's right. A new and dangerous threat. Thank you, martha raddatz.
This transcript has been automatically generated and may not be 100% accurate.