

"It does not look like U.S. devices, to be sure, but it is hard to know if aspects of the model are truly implausible or simply that North Korean nuclear weapons look different than their Soviet and American cousins," Lewis wrote in an analysis for 38 North, a website devoted to North Korea. "The size, however, is consistent with my expectations for North Korea."



As international condemnation of the North's acts mounted, culminating in the toughest U.N. sanctions against Pyongyang yet, Kim's regime has become increasingly belligerent, firing missiles into the Sea of Japan, also known as the East Sea, and issuing a new threat or denunciation almost every day.



The sanctions coincide with annual spring drills between the U.S. and South Korean militaries, which Pyongyang considers a rehearsal for an invasion. The current exercises are particularly antagonistic because special forces are practicing "decapitation strikes" on regime leaders and taking out nuclear and missile sites.



On Friday, North Korea's state media reported that Kim had ordered more nuclear tests, while the North's Korean People's Army warned in a statement Saturday that it would counter the drills by "liberat[ing] the whole of South Korea including Seoul ... with an ultra-precision blitzkrieg strike of the Korean style."



South Korea's Defense Ministry urged Pyongyang to stop its threats and provocations.



"If the North continues to make provocations despite the stern warnings made by our military, it is inevitable for us to roll out a strict response that may lead to the destruction of the Pyongyang regime," South Korea's Joint Chiefs of Staff said in a statement, according to the Yonhap News Agency.