Last month, North Korea launched a long range ballistic missile, considered by many Western countries as a provocative act.
The North Korean missile is called the Taepodong-2. Analysts say it theoretically has a range of between 3,600 and 4,300 kilometers, making it capable of reaching the western United States.
Paul Carroll is a nuclear weapons and North Korea expert at the San Francisco-based Ploughshares Fund, which supports initiatives to prevent the spread and use of nuclear weapons. "It's a three-stage rocket, which is basically what you would need to put something into orbit -- also what you would need to successfully launch or send a warhead of some kind through space to another continent. My understanding from technical observers and experts is that the first stage was successful. The first stage ignited and launched and landed where the North Koreans said it would land. The second stage, however, failed to complete its burn period and, as a result, fell quite short of where the North Koreans had anticipated that it would land. And not only that, it meant that the third stage didn't get anywhere. Essentially, it just splashed down into the Pacific [Ocean]," he said.
Western officials described the test as a failure. But North Korea called it a success, saying the rocket launched a communications satellite into orbit.
Why did Pyongyang test launch such a rocket at this time?
"It is consistent with their behavior of when they feel ignored -- they are not getting the attention, they are not getting what they want, of creating a crisis which they expect the United States and the Chinese, to a lesser extent, to respond to by re-engaging and moving towards whatever objective they want to have," said David Kay, the former chief nuclear weapons inspector for the International Atomic Energy Agency.
Jim Walsh, a North Korea and nuclear weapons expert at the Massachusetts Institute of Technology, or MIT, sees another reason.
"There is the notion that North Korea may be going through the first steps of a succession process. Remember, their leader, Kim Jong Il, had a stroke. And there's talk about them reshuffling the leadership and starting to think about a post-Kim regime. And the rocket launch may have been tied to that," he said.
The launch brought international condemnation, although North Korea has stated it has the right to conduct such tests.
The United Nations issued a statement condemning the rocket launch. The U.N. also imposed additional sanctions on three North Korean companies.
Pyongyang reacted by withdrawing from the six-party nuclear disarmament talks and threatening to conduct a nuclear test. It also expelled international nuclear inspectors and announced that it would begin reprocessing plutonium from its Yongbyon facility -- a first step in building nuclear weapons.
Kay says the small, five megawatt, Yongbyon reactor complex is in various stages of disrepair.
"The North Koreans, under the terms of the six-party agreement worked out with the United States and the others, have, in fact, demolished the cooling tower and disassembled other parts of the reactor. So putting the reactor back in operation is probably a two year effort. On the other hand, the reprocessing cells, where the plutonium would be separated out, are in a better state of repair and probably capable -- given relaxed safety standards in North Korea -- of being used almost immediately," he said.
Experts say there are two ways to make fissile material for nuclear weapons. One way is by enriching uranium. The other is to reprocess plutonium -- the method chosen by North Korea.
Walsh says it is difficult to know how many nuclear weapons North Korea actually has. "Estimates going back to the early 1990s, when the crisis first came into public view, suggested that North Korea could have anywhere from zero -- because we weren't sure -- zero nuclear weapons to maybe five nuclear weapons. And over the decade-and-a-half since then, that number has slowly risen to anywhere from five to 12, something like that. We're still talking about a relatively small number of nuclear weapons," he said.
Many experts say the best way to address Pyongyang's nuclear weapons program is to revive the six party talks -- bringing together the United States, China, Japan, Russia, South Korea and North Korea. But they say even before that happens, the first order of business will be to convince North Korean officials to return to the negotiating table since they have decided to boycott the talks after worldwide criticism of their long range missile test.