North Korea's threat to launch a preemptive nuclear strike against the United States has puzzled American officials, who see the regime ramping up its threats and rhetoric.
It's leading to the belief that North Korean leader Kim Jong Un is more unpredictable, more dangerous and harder to read than his late father, Kim Jong Il.
"The new leader is acting in ways a bit more extreme than his father, who was colder and more calculated," a senior administration official said. "Kim Jong Il was more aware of the off-ramps to end these escalations.
"I don't recall he ever went this far in terms of the pace and scope of the rhetoric. Threatening to launch nukes directly against the United States and South Korea confirms what a lot of people have been saying, which is we are dealing with someone new," the official added.
Comparing Kim Jong Il, who died last December, to a chess player, the official said the son is more like a boxer.
"Nobody knows what he has planned, what he is thinking or contemplating doing or why the North Koreans are tripling down on their rhetoric," the official said.
Another senior administration official said Kim's youth and education abroad offered promise for many North Korea watchers that he would be more willing to engage with the West.
"Unfortunately, he is following the example of his father and grandfather pretty closely," the official said. "It's hard to be optimistic."
His grandfather, Kim Il Sung, was the founding leader of North Korea.
Officials said the latest threats, coupled with North Korea's nuclear test last month and its launch of a long-range rocket into space in December, have the United States and South Korea bracing for the possibility of a violent response by Pyongyang to tougher U.N. sanctions approved on Thursday.
They pointed to the 2010 sinking of a South Korean submarine and shelling of a South Korean island.
"It's dangerous to dismiss these threats as just rhetoric and propaganda, the second official said. "It's hard to predict."
Leading up to the U.N. vote, North Korea upped its bellicose rhetoric.
A spokesman for the foreign ministry suggested the United States "is set to light a fuse for a nuclear war."
As a result, North Korea "will exercise the right to a preemptive nuclear attack to destroy the strongholds of the aggressors and to defend the supreme interests of the country," the country said in a statement carried by the state-run Korean Central News Agency.
Despite the strong language, analysts say North Korea is years away from having the technology necessary to mount a nuclear warhead on a missile and aim it accurately at a target. And, analysts say, North Korea is unlikely to seek a direct military conflict with the United States.
North Korea's behavior is even more curious because it comes as South Korea's new president, Park Geun-hye, took office last week calling for new dialogue with the North. Although she pledged a strong defense posture and retaliation against North Korean provocations, she called for easing tensions that grew under her predecessor.
"Given that for five years they were so angry at the previous president, Lee Myung-bak, why would they mortgage the next five years by being so difficult when a new South Korea leader is just taking office," the first official asked. "It's so very concerning."
Officials note that China, North Korea's closest ally, has demonstrated unprecedented frustration with Pyongyang's behavior.
In rare public statements, a top Chinese Communist party official suggested that China abandon North Korea and support unification with South Korea.