How big a threat is North Korea?

North Korea has raised the stakes on the Korean peninsula by conducting an underground nuclear weapon test Monday and subsequently test-firing half a dozen short-range missiles. The rapid sequence of events is creating a new sense of crisis in Asia and fresh concerns about the proliferation of nuclear weapons technology.

North Korea has been reprocessing spent fuel rods to produce weapons-grade plutonium at its central nuclear complex at Yongbyon since the 1980s. North Korea now is believed to have enough reporcessed plutonium for at least half a dozen nuclear warheads. Although no one knows for sure how many warheads the regime has fabricated or even where they are, North Korea has now detonated two of them. The first test, in October 2006, measured less than one kiloton, a weak blast likely due to problems with the design or materiel.

The second device was more powerful than the first, estimated at between 1.5 and 4 kilotons. That's still not as powerful as the 15-20 kiloton bombs dropped on Hiroshima and Nagasaki in August 1945, as initially claimed in a Russian news report about Pyongyang's latest test. The speed with which North Korea exploded the second nuclear device after vowing to "bolster" its nuclear deterrent suggests that it has more bombs ready for testing.

North Korea is believed to be working to develop a warhead small enough to fit on the tip of a long-range missile. Some experts say that North Korea has already created nuclear warheads for medium-range Nodong missiles that could strike South Korea and Japan, and has stockpiles of medium- and short-range missiles.

North Korea launched a Taepodong long-range missile in 2006 that fell into the sea 40 seconds after launch. The Taepodong-2 launched April 5 was more successful, traveling 2,000 miles over Japan and falling into the Pacific Ocean, though it did not have the range to reach US territory. Eventually, however, this missile might be able to go as far as the Hawaiian islands, Alaska – or even the US West Coast.

But short of having the ability to reach US territory, part of North Korea's strategy may be to become enough of a threat to its neighbors that the US is hesitant to commit to defending them, says Sheila Smith, senior fellow for Japan studies at the Council on Foreign Relations.

"The North Koreans are willing, within limits, to use capabilities they do have to create instability within the region," says Ms. Smith. "There is a potential here of discriminating between the US and its allied partners in the region.... The main aim of the North Korean missile program is to delink the US from its willingness to defend Japan."

North Korea has sold its missile technology to Iran, Yemen, Syria, and Pakistan's Abdul Qadeer Khan, who has admitted to providing regimes around the world – including North Korea – with nuclear information. Experts believe the cash-starved nation has shared its nuclear know-how and imported technology and materiel from Mr. Khan's network.

"There is an indication that [North Korea's] main focus is on the possibility of export as a vehicle by which to increase their access to foreign currency," says Scott Snyder, director of the Center for US-Korea Policy at the Asia Foundation.

It is widely believed that a nuclear reactor recently constructed in Syria – and destroyed by Israeli airstrikes in October 2008 – was built with assistance from North Korea. Some also believe that the North is providing a small research reactor to Burma (Myanmar), says Daniel Pinkston, Northeast Asia deputy project director for the International Crisis Group.

He says the likelihood of North Korea providing nuclear assistance or devices to nonstate terrorist groups like Al Qaeda is unlikely, due to the difficulties of such a transaction. And if the goal of such a group was a bomb, the design of choice is a uranium bomb, which North Korea has not yet produced, says Mr. Pinkston.

"You can't rule it out, but I think it's a low-probability event," Pinkston says. "If you are interested in cash or cooperation, why would you bother with that?"

But Mr. Snyder says the risk of nonstate actors getting their hands on North Korea's nuclear material or technology is a concern.

"North Korea has made it known that they're willing to sell anything to anybody, and they're pretty desperate in terms of their economic situation," he says. "If they can find a buyer and they can assess that the risk is not too great in terms of being caught, I think they would consider a deal."

Might North Korea inspire a nuclear arms race?

Japan and Taiwan are believed to be well on their way to acquiring all the expertise needed to develop nuclear devices of their own. They both have nuclear power plants and scientists and engineers with vast experience in the field. The emergence of North Korea as a nuclear power could spur them to cast aside restraints and go nuclear militarily. South Korea also may be tempted – though the US over the years has severely restrained South Korean scientists.

Where is North Korea going from here in nuclear development?

The Yongbyon complex – believed to be able to produce about a bomb's worth of weapons-grade plutonium in a year – is no doubt old, but North Korea also is working on developing warheads using enriched uranium. It has other facilities hidden away, and it has acquired materiel – notably centrifuges – from Pakistan and elsewhere. Iran's nuclear program is all uranium, and North Korea is assumed to be sharing information and components with Iran.

Are domestic considerations a factor in North Korea's tests of nukes and missiles?

North Korea's leader, Kim Jong Il, is clearly ill, and reportedly suffered a stroke last August. Many observers say that he is attempting to pass on power to his youngest son, still in his 20s, while fending off a power drive from his generals. Mr. Kim rules through his National Defense Commission, of which he is chairman, and he has been promoting the "military first" policy for years. Observers say that the nuclear and missile programs represent an effort to assert his own authority before his death. He may have a goal of securing Korth Korea's status as a global nuclear power by 2012 – the 100th anniversary of the birth of his father, Kim Il Sung.