PYONGYANG, North Korea - The North Korean army is warning Washington that its military has been cleared to wage an attack using "smaller, lighter and diversified nuclear" weapons.
The threat from the unnamed army spokesman early Thursday is latest in a series of escalating warnings from North Korea, which has railed for weeks against joint U.S. and South Korean military exercises taking place in South Korea and has expressed anger over tightened sanctions for a February nuclear test.
The spokesman said in a statement carried by the Korean Central News Agency that troops have been authorized to counter U.S. aggression with "powerful practical military counteractions."
Dr. Richard Moeller, a national security exert and political science professor MSU Denver, said that while the threat must be taken seriously, it is unlikely North Korea has the capability to follow through with it.
"It all boils down to limitations and capabilities," said Moeller, "And the United States has great capabilities in the region and North Korea has great limitations. And because of that, I think, this is more hot air than anything else."
Moeller said Kim Jong-un's rhetoric is more about internal politics, convincing hard liners in his own country that he is a competent leader who could one day re-acquire South Korea.
"The international community has not really been effective in ostracizing him, and I think that is emboldening him in order to try to achieve greater things," said Moeller. "This is a dynastic dictatorship, meaning grandfather to father to now grandson. And if he feels any tension at home threatening that, he could do something like he's doing right now in order to prove that he is worthy of this dynastic destiny that he's been given."
Acting on one of its threats, North Korean border authorities have refused to allow entry to South Koreans who manage jointly run factories in the North Korean city of Kaesong. Trucks carrying cargo and South Korean workers were turned back Wednesday and again Thursday morning.
This spring's annual U.S.-South Korea drills have incorporated fighter jets and nuclear-capable stealth bombers, though the allies insist they are routine exercises. Pyongyang calls them rehearsals for a northward invasion.
The foes fought on opposite sides of the three-year Korean War, which ended in a truce in 1953. The divided Korean Peninsula remains in a technical state of war six decades later, and Washington keeps 28,500 troops in South Korea to protect its ally.
Hagel said Washington was doing all it can to defuse the situation, echoing comments a day earlier by Secretary of State John Kerry.
"Some of the actions they've taken over the last few weeks present a real and clear danger and threat to the interests, certainly of our allies, starting with South Korea and Japan and also the threats that the North Koreans have leveled directly at the United States regarding our base in Guam, threatened Hawaii, threatened the West Coast of the United States," Hagel said Wednesday.
In Pyongyang, the military statement said North Korean troops had been authorized to counter U.S. "aggression" with "powerful practical military counteractions," including nuclear weapons.
"We formally inform the White House and Pentagon that the ever-escalating U.S. hostile policy toward the DPRK and its reckless nuclear threat will be smashed by the strong will of all the united service personnel and people and cutting-edge smaller, lighter and diversified nuclear strike means," an unnamed spokesman from the General Bureau of the Korean People's Army said in a statement carried by state media, referring to North Korea by its formal name, the Democratic People's Republic of Korea. "The U.S. had better ponder over the prevailing grave situation."
However, North Korea's nuclear strike capabilities remain unclear.
Pyongyang is believed to be working toward building an atomic bomb small enough to mount on a long-range missile. Long-range rocket launches designed to send satellites into space in 2009 and 2012 were widely considered covert tests of missile technology, and North Korea has conducted three underground nuclear tests, most recently in February.
"I don't believe North Korea has to capacity to attack the United States with nuclear weapons mounted on missiles, and won't for many years. Its ability to target and strike South Korea is also very limited," nuclear scientist Siegfried Hecker, a senior fellow at the Center for International Security and Cooperation at Stanford University, said this week.
"And even if Pyongyang had the technical means, why would the regime want to launch a nuclear attack when it fully knows that any use of nuclear weapons would result in a devastating military response and would spell the end of the regime? " he said in answers posted to CISAC's website.
In Seoul, a senior government official said Tuesday that it wasn't clear how advanced North Korea's nuclear weapons capabilities are. But he also noted fallout from any nuclear strike on Seoul or beyond would threaten Pyongyang as well, making a strike unlikely. He spoke on condition of anonymity because he wasn't authorized to speak publicly to the media.
North Korea maintains that it needs to build nuclear weapons to defend itself against the United States. On Monday, North Korean leader Kim Jong Un led a high-level meeting of party officials who declared building the economy and "nuclear armed forces" as the nation's two top priorities.