For weeks, North Korea and the West have been engaged in a largely symbolic ratcheting up of tensions.
But Pyonyang's announcement on April 2 that it will restart its Yongbyon nuclear reactor, closed since 2007, goes far beyond its recent declaration that it is in a "state of war" with Seoul or its retargeting of missiles toward U.S. bases.
That is because restarting Yongbyon reactivates North Korea's ability to produce nuclear weapons -- something the West once thought was largely contained.
Nuclear experts say that North Korea is assumed to have six to eight nuclear weapons. They are assumed to be made of plutonium extracted from spent fuel rods at the Soviet-era Yongbyon research reactor before it was closed in 2007 under a disarmament-for-aid deal with the West.
That deal later fell apart amid U.S. suspicions that Pyongyang was not fully disclosing all of its nuclear activities, including further plutonium extraction and the construction of a clandestine uranium-enrichment facility.
It is still unknown what kind of nuclear device North Korea tested in February -- the event that sparked the current crisis. But according to Paul Rogers, a nuclear expert at Bradford University in England, there is some speculation that it was made of secretly enriched uranium.
If this is the case, Pyongyang's decision now to openly restart the reactor may suggest it still feels a need to produce more powerful plutonium weapons as well.
"Enriched uranium in some ways produces rather cruder weapons, so the decision to restart the nuclear reactor is really quite significant," Rogers says."It does indicate that North Korea now wants to build a more sizable and potentially more usable nuclear arsenal."
Reactor In A 'State Of Disarray'
Plutonium bombs are more powerful than enriched-uranium bombs and easier to miniaturize into warheads. North Korea already has an active missile development and testing program, but is not yet believed to have a way to deliver nuclear weapons other than by airplane.
Just how quickly North Korea can start its Yongbyon reactor is uncertain.
Shannon Kile, a nuclear expert at the Sweden-based Stockholm International Peace Research Institute, maintains that the reactor was deliberately disabled under the aid-for-disarmament deal.
"I am very skeptical whether they are going to be able to [reactivate the reactor]," he says. "The last IAEA (International Atomic Energy Agency) visit there in 2009 indicated the place was a complete shambles. [The North Koreans] blew up the cooling tower in 2008 and, by all accounts, the reactor complex, the plutonium production reactor, is in a state of disarray. It is not clear that it can be repaired."
Kile suggests that when Pyongyang announced it would restart the Yongbyon reactor it most likely meant it will restart other, associated facilities at the site.
That includes a plutonium-separation facility which could be revived to process any remaining stockpile of plutonium that Pyongyang has.
It also includes a new light-water reactor that is under construction and would create plutonium among its byproducts.
In addition to these plutonium facilities, Kile believes Pyongyang will continue to focus on developing designs for smaller, more compact, enriched-uranium weapons that could be carried by ballistic missiles.
As Pyongyang ramps up the stakes in its current crisis with Seoul and Washington, there is much debate over its motives.
Many analysts believe that North Korea was infuriated by the latest round of UN sanctions placed on it in the wake of its February nuclear test.
A New Leader Earning His Spurs?
But the timing of the crisis also suggests it may serve the needs of North Korea's new young leader, Kim Jong Un, to mobilize support among the country's military elite. Kim, believed to be 30 years of age, was declared supreme leader following the death of his father, Kim Jong Il, in late 2011, and was not prominent before that time.
"A great deal of this is about Kim Jong Un's need to prove himself," says Aidan Foster-Carter, a Korea expert at Leeds University in England. "He has only been in power for a little over a year. He is untried; he had all too little time to prepare, unlike his late father Kim Jong Il, who was being groomed for the job for about 20 years."
There also has been speculation that Pyongyang may use its revived nuclear program to one day negotiate a new aid-for-disarmament deal with the West.
But Kile believes that restarting Yongbyon, after the previous deal broke down, suggests that Pyongyang has made up its mind to become a bigger nuclear power.
"It seems to me North Korea is determined to move ahead with its nuclear arsenal," he says. "They are going to improve it both in terms of numbers but also in terms of the types of weapons they have at their disposal and I don't think that they are going to be willing to back down from that for any sort of international humanitarian assistance."
North Korea, despite its powerful military, is one of the world's poorest countries and has long received various levels of UN food assistance to protect its population from starvation.