SEOUL North Korea's nuclear test on Monday sparked international condemnation. Following are some questions and answers about why the North went ahead with the test and why it came sooner than analysts had expected.
WHY DID NORTH KOREA CHOOSE TO TEST NOW?
North Korea likely concluded that no concessions would flow from U.S. President Barack Obama, especially after his strongly worded response to Pyongyang's rocket launch last month that regional powers say was a long-range missile test. To North Korea, this probably signaled Washington was in no mood for direct negotiations, something long sought by Pyongyang.
The North may have also felt it needed to boost its leverage by conducting a follow-up nuclear test after its only other test nearly three years ago was considered just a partial success.
North Korean leader Kim Jong-il, perhaps pressured by an ailing economy and questions about succession, may be trying to lure Washington into making a quick deal that would boost his standing at home.
Monday was the Memorial Day holiday in the United States, and the test follows a pattern of Pyongyang's provocations timed for U.S. national holidays. The 2006 test of North Korea's long-range Taepodong-2 missile came on the U.S. Independence Day holiday.
ARE THERE DOMESTIC FACTORS AT PLAY?
Kim is returning to the center stage in Pyongyang after a long absence from the public view following a suspected stroke last August. His illness has focused attention on who might take over in Asia's only communist dynasty.
Analysts said the recent demonstrations of military strength might make it easier for Kim to introduce one of his three sons as a successor when most of the North Korean public is unaware he even has children. The recent saber rattling could also divert attention from the country's economic malaise.
North Korea says it has been on a 150-day "battle" leading up to the October 10 anniversary of the ruling Workers' Party, and the nuclear test has been a major part of the propaganda campaign.
There is a possibility the North will follow up with an additional nuclear test before the 150-day campaign is over, although this would risk depleting its meager stockpile of fissile material.
Nuclear experts say at least as many as half a dozen nuclear tests are needed to accomplish the technology for a stable and workable nuclear device and it may take years for the North to build a weapon it could mount on a ballistic missile.
DOES NORTH KOREA WANT TO BE A NUCLEAR STATE?
It appears so. For a country with a battered economy and food shortages that make it reliant on outside aid to feed its people, a nuclear arms program is the ultimate bargaining chip to win concessions from the United States and regional powers.
The more nuclear advances it makes, the greater the payoff it expects in negotiations with countries willing to pay for the North's eventual disarmament, if that ever happens.
South Korea, Japan and the United States say they will never recognize the North as a nuclear state and consider its moves to achieve such a status a grave threat to regional security.
SO WILL NORTH KOREA RETURN TO DISARMAMENT TALKS?
This is unlikely at the moment. North Korea has said six-way disarmament talks are over because U.N. sanctions against its April rocket launch infringed its sovereignty and nullified all deals reached under the multilateral talks, which began in 2003.
Officials in Seoul and analysts have expressed concern that the six-way talks among the two Koreas, the United States, Japan, Russia and China may indeed be over in their current form.
(Editing by Jon Herskovitz and Dean Yates)