North Korea today signaled its determination to go through with a third nuclear test in the face of warnings from friends and foes alike.

Today on the 80th anniversary of the founding of the North Korean armed forces, Vice Marshal Ri Yong-ho said North Korea now had mobile weapons that were strong enough to strike targets in the US.

That boast appeared to refer to North Korea’s development of long-range missiles that should theoretically be able to deliver a nuclear warhead as far as the US West Coast. Mr. Ri indicated the North’s intention to miniaturize nuclear devices in order to fit them on the missile by claiming that the North could deal a devastating defeat in “a single blow.”

The North Korean rhetorical blast, as reported by Pyongyang’s Korean Central News Agency, is the latest in a flood of invective, most of it directed against South Korea’s President Lee Myung-bak and his government. The rhetoric leaves little doubt for most analysts that North Korea sees the test as needed to compensate for the humiliation suffered on April 13 when its vaunted long-range rocket broke up and plunged into the Yellow Sea 90 seconds after it was launched.

North Korea also has more practical military and political reasons for wanting to conduct the test in defiance of diplomatic efforts to persuade its new leader, Kim Jong-un, to call off the project.

“There’s a military imperative,” says Mark Fitzpatrick, a former US State Department official now with the International Institute for Strategic Studies in London. Mr. Fitzpatrick says the North’s first two underground nuclear tests, in October 2006 and again in May 2009, “did not go very well.”

Although North Korea did manage to explode nuclear devices on both occasions, they were so small as to have been viewed by scientists elsewhere as a possible failure.

What North Korea wants

North Korea’s top priority now is to be able to miniaturize a warhead in order to send it to a target on a missile rather than drop it as a bomb from a plane. “They want to get something small enough to fit on a Rodong,” says Mr. Fitzpatrick, at a conference here staged by the Asan Institute, a local think tank financed by the Hyundai business empire.

Yet another issue is the need to convince the North Korean people that Kim Jong-un is a strong leader, capable of controlling a military establishment with 1.2 million troops while solidifying his power over the country.

“Having failed on the missile, they’ve got to do something that goes boom,” says Fitzpatrick.

The decibel level of the North Korean rhetoric is beginning to raise alarm here among analysts who fear the North may challenge South Korea with incidents to which the South will have to respond militarily.

President Lee has vowed that South Korean forces will strike back militarily if the North stages an attack similar to the shelling of Yeonpyeong Island in the Yellow Sea in November 2010 in which two marines and two civilians were killed. That attack came 10 months after the sinking in nearby waters of a South Korean navy ship in which 46 sailors were killed.

Motivating factors for a third nuclear test, says Kim Tae-woo, president of the Korea Institute for National Unification, are North Korea’s desire to demonstrate its place as a full-fledged nuclear power as well as the need to intimidate both the US and South Korea.

A demonstration of North Korea’s nuclear prowess, according to North Korean logic, would result eventually in the US agreeing to negotiations that might again result in promises of food aid.

After this month’s missile test, President Obama suspended plans to ship 240,000 tons of food to North Korea, but Kim Tae-Woo believes that the US might still be inclined to return to negotiations after the next presidential election.

Intimidation of South Korea also appears as key to North Korea’s strategy. North Korea wants to prove, “We are dominating North-South Korean relations,” says Kim Tae-woo.

That strategy assumes special importance considering that South Koreans in December elect a successor to President Lee, barred by the South’s constitution from seeking a second five-year term. The conservative Park Geun-hye, daughter of South Korea’s long-ruling Park Chung-hee, assassinated in 1979, is likely to be the conservative candidate but faces a tough fight from whoever wins the nomination of the opposition Democratic United Party.

China 'on the hot seat'

The question many observers ask is whether China, as the source of most of North Korea’s fuel and much of its food, can play a role in dissuading North Korea from investing so heavily in missiles and nuclear devices.

“The Chinese are on the hot seat,” says Christopher Hill, former US envoy in negotiations with North Korea, now at the University of Denver.

Mr. Hill sees little real difference between policies under Kim Jong-un and those led by his father, Kim Jong-il, who died in December. “The idea that Kim Jong-un is going to back out of this system is a little far-fetched,” he says. “You have a military-first system where the military calls the shots.”

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If only “the US and China would work together and resolve this problem,” Hill says, “it would have an enormous impact on Sino-US relations.”

In the meantime, analysts try not to be overly alarmed by North Korean rhetoric. “As long as it’s just words, everything’s fine,” says Scott Snyder of the Council on Foreign Relations. “We will be concerned if it escalates into actions.”