i think the united states and the world community needs to act with resolve. >> ifill: siegfried heckerll us what is possible for north korea to have pulled off in this case? >> it's not clear exactly what they did. as sherman pointed out, they did a nuclear test. my greatest concern is they did the fourth nuclear test. with that nuclear test, they clearly achieved greater sophistication and most likely meaning being able to make the bomb smaller, lighter and, therefore, have greater reach if they're able to get them on a missile. whether it was a hydrogen test or not, we don't know. my sense is we probably never will really know. so far from the information that's there, it appears the size of the blast -- in other words, the power from the seismic signal that can be measured -- it's about the same level as the third nuclear test in 2013, which with we put at the level of approximately a hiroshima bomb, let's saying 10 to 15-kilotons. now, whether it actually achieved the sophistication of going to a fusion bomb. the fusion or hydrogen bomb is a very big step technologically, and it's

where the scientists are incredibly nervous, for instance, the great american nuclear scientist siegfried hecker the only americans that gets regular access into its nuclear facilities, into china, sits there with all sorts of officials from around the world and sees firsthand and is able to give the best case assessment of what's going on in that secretive nation. last year he warned very, very clearly that this was on track. >> the chinese have also a great set of eyes on the situation and know as well as any who are going on. how important are they? supposedly they're going to come out and give a condemnatory statement. >> the chinese are the closest associated not only the closest associates but also close physically to north korea. in the past have had a lot of influence on north korea but since xi jinping became president they've been much tougher on north korea and they've had much less influence and much less connection, particularly with the current leader, kim jong-un. that's a problem there. some believe that maybe their influence is slightly less than it should be and that it was. bu