What's the threat? North Korean rhetoric, reality

Despite December's successful launch, North Korea's ability to get missiles off the launch pad is less than reliable. In April, a similar rocket splintered into pieces over the Yellow Sea. Days later, North Korea showed off what appeared to be an intercontinental ballistic missile, but many experts who reviewed footage of the rockets said they were clearly fakes.

The North does, however, appear to be making some progress.

Japan's Defense Ministry, in an assessment of the December launch presented to the prime minister on Friday, said the North's best designs probably give its missiles a range of more than 10,000 kilometers (6,200 miles), according to Japan's Kyodo news service. That would be enough to reach the West Coast of the United States. A South Korean defense official said Friday that Seoul agrees with that assessment.

The Japanese report warned that Pyongyang's missile technology has "entered a new stage" that is of serious concern to the international community. Japan is particularly wary of North Korea's capabilities because all of its islands are well within striking distance. Japan also hosts about 50,000 U.S. troops, whose bases would be a tempting target if Pyongyang were to try to make good on its threats.

"There has been a tendency to underestimate what North Korea can do in the space and missile field, and possibly with technology in general," U.S. nuclear expert Jeffrey Lewis wrote recently on his Arms Control Wonk blog. He noted that debris recovered from the wreckage of the December rocket's first stage indicates that most of it was made in North Korea.

North Korea claims the right to build nuclear weapons as a defense against the United States, which stations more than 28,000 troops in South Korea.

It is believed to have enough weapons-grade plutonium for about four to eight bombs, according to nuclear scientist Siegfried Hecker, who visited North Korea's nuclear complex in 2010. And in 2009, Pyongyang also declared that it would begin enriching uranium, giving it a second way to make atomic weapons.

U.S. Defense Secretary Leon Panetta said Thursday that he has seen no outward sign that North Korea will follow through soon on its plan to conduct a test, but added that doesn't mean preparations aren't under way.