Xinhua/KCNA/Xinhua Press/Corbis

A view of the launch of North Korea's Kwangmyongsong-3 satellite from the Pyongyang General Satellite Control Command Center on Dec. 12, 2012. Xinhua/KCNA/Xinhua Press/Corbis

Thursday, North Korea stated explicitly that in addition to planning a third nuclear test, it would also be "targeting" the United States with its nuclear program.

But although the Democratic People's Republic of Korea has rockets and an active nuclear program, threats of a nuclear attack may be bluster, according to some experts – at least for now.

Hans Kristensen, director of nuclear information at the Federation of American Scientists, told Discovery News. "They've built some devices that can go off," he said. "That's not the same as a bomb."

PHOTOS: World's Worst Prisons

There are three parts to making a nuclear weapon, he said. First is the fissile material -- uranium and plutonium. The second is the ability to get a bomb onto a plane or missile. Last is designing a missile that will reach targets as far away as the continental United States. North Korea has the first, has not shown it has the second and is part way towards the third.

North Korea showed it had the fissile material when it set off two test explosions, one in 2006 and one in 2009. Most experts consider the first a failure, given that it was only the equivalent of 1,000 tons of TNT, or one kiloton. The 2009 explosion was more successful, estimated at several kilotons -- still a fraction the power of the bomb used on Hiroshima.

Setting off a nuclear explosion is one thing, but building a warhead small and light enough to fit in a plane or on top of a missile is another. For comparison, it took the United States several years to develop warheads that could fit on a rocket. "The first hydrogen bomb we dropped on test sites in the Pacific was the size of a small house," said Kristensen. That was in the 1952. A missile capable of sending a bomb to the USSR wouldn't debut until 1959.

PHOTOS: Dangerous Tourist Destinations

If the North Koreans can shrink a bomb down to that size, they would still need a long-range missile. So far the DPRK has test-flown several missiles of varying ranges. This past December, they launched a satellite, which is reportedly spinning out of control. North Korea has launched satellites before: in 2009 with the Kwangmyŏngsŏng-2, which the government said was a communications satellite, and in 2006 it conducted a test of several missiles, among them the Taepodong-2, which failed seconds after lift-off.

Although none of the missiles or rockets successfully tested so far could reach the continental United States, it's possible that the North Koreans could develop one. Current estimates for the range of a Taepodong-2 are as much as 6,200 miles, enough to reach the western half of the United States. That estimate is at the high-end and assumes the missile has a two-stage rocket.

A satellite image of the Punggye-ni Nuclear Test Facility in North Korea, collected on October 29, 2012, confirms reports that new construction is underway within the facility.DigitalGlobe via Getty Images

The missile technology, however, is missing a crucial piece, said Kristensen: the re-entry vehicle. Any intercontinental missile designed to travel from North Korea to Alaska or Hawaii needs to leave the upper atmosphere, and that means the warhead has to have shielding for when it comes back to earth to hit its target. Without it, the warhead burns up before it reaches the ground. Bits of radioactive debris might survive, but not much else.

"You just don't see the elaborate re-entry vehicle tests," Kristensen said. And that wouldn't be a secret – there is simply no way to hide such a launch. "We've spent the last 60 years monitoring every single Russian test," he said. North Korean tests are just as visible. Even preparing for one would be obvious because of the sheer size of the industrial plant involved, to say nothing of the size of the rocket.

"If I were the North Korean leader and desperate for a weapon, I'd attach it to an aircraft," said Kristensen. "A ballistic missile is the most complicated way to develop a weapon." The North Koreans haven't announced that they have a bomber capable of carrying a nuclear bomb – which would be a much more credible threat.

PHOTOS: World's Worst Prisons

None of this means that the North Koreans couldn't develop these technologies in the future, but it will probably be some time.

David Straub, associate director of Korean Studies Program at Stanford University's Freeman Spogli Institute for International Studies told Discovery News that in 2011 then-Secretary of Defense Robert Gates said the direct threat to the United States would come in about five years. That means 2016.

Between now and then the DPRK would have to test more rockets, of multiple stages, as well as re-entry vehicles.

The country at the most risk is likely South Korea. In the meantime the North Koreans have threatened South Korea with "strong physical countermeasures" if it takes part in U.N. sanctions designed to punish the North for the missile tests. North Korean missiles could certainly hit targets in South Korea or even Japan with a nuclear warhead, if they have managed to build one small enough. But both Straub and Kristensen agreed that would be against Kim Jong-un's best interest. "The regime wants to survive," said Straub.

PHOTOS: Dangerous Tourist Destinations

In the end, however, the real audience for such announcements may well be inside North Korea. Standing up to the United States is a good way to make the regime look like it is defending the North Korean people against a potential threat, and distracts from problems at home such as a moribund economy and persistent shortages of food and fuel.

And they aren't likely to give up, said Straub. "North Korea been pursuing and working on nuclear programs for a long time," he said. "They've invested a lot of time, a lot of energy a lot of attention at the highest levels."