MULLEN: Well, I think we have to continue to bring pressure on him specifically. Those in the region -- in particular the six-party talk countries, Russia, China, the United States, Japan, and South Korea, we all -- we have to continue to do that.
He is predictable in his unpredictability, if you will, because not too long ago, he killed 46 South Korean sailors. He has over time continued to destabilize this region. And, in fact, I also believe that this has to do with a succession plan for his son.
AMANPOUR: But do you think they're planning to make more nuclear weapons? What do you think they're trying to do? And again, if sanctions aren't working, what will?
MULLEN: Well, the assumption certainly is, that they continue to head in the direction of additional nuclear weapons. And they're also -- they also are known to proliferate this technology.
So they're a very dangerous country. And -- and he has been someone who has not responded thus far to previous actions. He actually blows hot and cold. He moves in a direction for a while, and then he reverts, and I certainly would see him in his reversion mode at this particular point in time.
AMANPOUR: And why didn't U.S. intelligence discover this?
MULLEN: Well, I won't go into any...
AMANPOUR: But isn't that alarming?
MULLEN: I won't go into any specific intelligence kinds of things today, Christiane, but I would say that, you know, this is something we've been concerned about for a significant period of time, and also penetration of -- of the North Koreans, in terms of intelligence capabilities, is very, very difficult.
AMANPOUR: Do you think China is the one to help you resolve this?
MULLEN: I think China has...
AMANPOUR: Will it?
MULLEN: ... an awful lot to do with that. We've been engaged with China for an extended period of time with respect to North Korea. The president sent out a team to each of the capitals this weekend to re-engage, and so that's where we are right now, and I'm sure we will continue to do that. And a great part of this, I think, will have to be done through Beijing.
AMANPOUR: Are you worried about North Korea making more nuclear weapons right now with this facility? Is that what it's showing?
MULLEN: I've been worried about North Korea and its potential nuclear capability for a long time. This certainly gives that potential real life, very visible life that we all ought to be very, very focused on.
AMANPOUR: The president and the president of Russia have signed the New START treaty. This week, that has been sort of stopped, stopping START in the Senate by the number-two Republican senator there, Jon Kyl.
Can I ask you -- I'm basically going to wave around a veritable "who's who" of Republican and Democratic former secretaries of state, of defense, all sorts of people who have been studying this for a long time and say that this has to be ratified. Does it have to be ratified? Is this necessary for U.S. national -- national security?
MULLEN: I think this is -- more than anything else, it's a national security issue. I was involved extensively in the negotiations with my counterpart in Russia. We have for decades have had treaties with them to -- to be able to -- to verify aspects of the nuclear weapons capabilities that we both have. And from a national security perspective, this is absolutely critical.