North Korea does not appear to be making preparations for a nuclear weapons test following Tuesday’s test of a space launch vehicle, which was believed to be cover for a long-range missile test, U.S. intelligence analysts told NBC News.

South Korean and Japanese officials had feared that a nuclear weapons test — its third after previous detonations in in October 2006 and May 2009 — would quickly follow the launch.

But word that the North isn’t thought to be preparing for a test is providing little solace for Seoul or Tokyo, mainly because recent intelligence suggests that the North has made significant advances in its nuclear weapons program.

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According to a recent analysis, North Korea has a weapon stockpile that could threaten both countries and, in longer term, the United States. Some of the weapons have already been deployed, say U.S. officials, speaking on condition of anonymity. Moreover, the North has begun research into more advanced and dangerous weapons, possibly even thermonuclear weapons, they say.  

 

At the high end of the stockpile range, U.S. officials and other researchers said North Korea may already have up to "a few dozen" nuclear weapons that could be fitted atop its vast fleet of ballistic missiles. Those missiles are limited to an intermediate range, capable of hitting targets in Japan, South Korea or elsewhere in the northern Pacific, including U.S. military bases as far south as Guam, the officials believe.

'Highly provocative'
The U.S. believes the space launch test is part of a development plan for an intercontinental ballistic missile (ICBM) capable of reaching the continental United States with a payload of several hundred kilotons — 10 to 20 times the size of the bombs that destroyed the Hiroshima and Nagasaki.

State Department spokesperson Victoria Nuland hinted about that Wednesday, calling the launch "highly provocative" and a "threat" to regional security. The U.S. is "concerned that all of this launching is about a weapons program and is not about peaceful uses of space," she added.

More North Korea coverage from NBC News

For the past several years, the U.S. also has been monitoring North Korean research into thermonuclear weapons — hydrogen bombs and bombs known as boosted fission weapons, in which plutonium and uranium are combined for a higher energy yield. (The problem is that if the North conducted a test and claimed that it was thermonuclear, the U.S. would have difficulty determining if the North was telling the truth. The test site at Kilchu is far enough inland that the U.S. would not have access to the particulate matter needed to make an accurate determination, experts say. )

David Albright, president of the Institute for Science and International Security, or ISIS, a nonpartisan nuclear arms research group, said earlier this year that any tests in the future may also be about ensuring the reliability of North Korea's current weapons design.

"Once you get beyond a dozen, it makes sense to test type and reliability of your weapons," he said. Albright said then that his group's estimate of North Korea's weapons stockpile is a bit less than those provided by the U.S. officials, but that ISIS, too, believes Pyongyang has "missile-deliverable weapons."

The design of the weapons is believed to be based on Chinese models (as were the first generation Pakistani nuclear weapons). The design is basic, and was developed in the 1960s with help from the Soviet Union, which used it to produce a whole line of nuclear warheads.

ANALYSIS: 'Spoiled child' North Korea snubs key ally China with rocket test

While some analysts suggest that the North is using its space rocket launch to gain attention ahead of next week’s presidential election in South Korea -- and possibly to force talks with the U.S. — some in the U.S. non-proliferation community think otherwise. They expect that once the North feels comfortable with its ICBM technology, it will deploy the missiles.  They point to the Musudan intermediate range missile which was tested in middle of the last decade, then deployed — presumably with nuclear warheads — and aimed at Japan. 

Once the North has confidence in the long-range missile based on the space rocket, U.S. officials believe they will deploy it as well, making North Korea the third nation to have nuclear weapons targeted at the United States, after Russia and China.

Many in the Obama administration see that as a more frightening prospect than Iran gaining nuclear weapons, believing that Tehran is a rational actor that will serve its own national interest and preserve the regime, compared to successive generations of North Korean leaders who have shown that they are unpredictable and erratic.

But would it force the U.S. turn to conduct face-to-face talks with the North? Nuland said Wednesday that the North has a better option.

Speaking of the North’s 27-year-old leader Kim Jong Un, Nuland said: "He can plot a way forward that ends the isolation, that brings relief and a different way of life and progress to his people, or he can further isolate them with steps like this. He can spend his time and his money shooting off missiles, or he can feed his people, but he can't have both."

Robert Windrem is a senior investigative producer for NBC News.

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