North Korea's second underground nuclear test has shown the world that it's only a matter of time before the secretive regime develops the ability to mount an atomic weapon on a missile.

Monday's blast — by all accounts larger than its first one in 2006 — indicates the impoverished country will keep using its nuclear development in efforts to bolster its regime and raise its stature against its main perceived adversary, the United States. It has also raised fears of increased proliferation.

North Korea's defiance in carrying out the latest explosion, which followed its first test in October 2006 that resulted in censure and sanctions by the United Nations, has met widespread condemnation and cast more doubt over the prospects for stalled talks aimed at the country's denuclearization.

President Barack Obama said the blast and North Korea's test firings of short-range missiles off its coast "pose a grave threat to the peace and security of the world," while Pyongyang answered Tuesday by launching more missiles. And on Wednesday, the North warned South Korea and the United States that Seoul's decision this week to participate in a U.S.-led program to intercept ships suspected of carrying weapons of mass destruction is equal to a declaration of war.

North Korea is believed to have processed enough plutonium over the years to have enough fissile material for at least half a dozen nuclear bombs.

That is paltry compared to the massive arsenals of nuclear powers such as the United States, Russia and China or even newer members of the atomic club like Pakistan.

Still, Pyongyang is making measurable progress and showing its determination to posses a credible enough threat to protect its regime, and it is unlikely to back down anytime soon given its increasingly strident tone on the world stage.

The North is now "more of a threat because they have more data and information about their bomb design," said Daniel Pinkston, a Seoul-based analyst for the International Crisis Group, a Brussels-based think tank devoted to conflict resolution. "They're demonstrating this decisiveness."

The size of the explosion is still under debate and will require more analysis to determine its actual size. Initial estimates have placed it between a few kilotons to between 10 and 20 kilotons by Russia's Defense Ministry.

The latter range, considered way too high by analysts including Pinkston and David Albright, president of the Institute for Science and International Security in Washington, would be comparable to the weapons that destroyed the Japanese cities of Hiroshima and Nagasaki during World War II.

Evidence suggests Pyongyang's ultimate goal is to mount a nuclear warhead on a missile, but analysts vary in their assessment of how close the country is to reaching this goal.

"It's a weapons program aimed at putting something on a missile to create a credible deterrent," said Albright of the ISIS. He said he thinks North Korea has the ability to mount a weapon now, though he added that questions remain about how reliable it would be.

Yoon Deok-min, a professor at South Korea's state-run Institute of Foreign Affairs and National Security, said North Korea appears still to be in the process of mastering the miniaturization technology required to mount a warhead onto a missile, though he called its ultimate success just "a matter of time."

He said its completion of a nuclear-tipped missile is the "worst case" security scenario, noting that the country has already deployed intermediate-range ballistic missiles that can travel as far as 1,860 miles (3,000 kilometers). That would easily put South Korea and Japan into range and almost reach the U.S. island of Guam.

What is disturbing, Yoon said, is that the country is conducting missile and nuclear tests in close proximity. Monday's blast came less than two months after the North fired a rocket over Japan and into the Pacific. Though Pyongyang claimed it was a satellite, the U.S. and other countries said the launch was meant to test ballistic missile technology.

Still, other analysts do not think that the North will imminently acquire the capability to master the delivery of a warhead. Cha Du-hyeogn, a research fellow of the state-run Korea Institute for Defense Analyses, estimates it may take about four years to accomplish.

Pinkston said that if analysis of the blast ultimately reveals that it was at the lower end of the yield range given so far, perhaps as small as three kilotons, that might suggest "they are working on miniaturization."

Ivan Oerlich, vice president of the Strategic Security Program at the Federation of American Scientists, said that early signs indicate that the test was much larger than the one in 2006, though far smaller than the Russian estimate.

The question of "is it a success depends largely on what they got compared to what they were hoping," Oerlich said.

Nuclear proliferation fears related to North Korea's nuclear program have also increased as a result of the test, analysts said.

"The proliferation part of this is more worrisome than being hit by a North Korean nuclear weapon," Albright said, noting that Pyongyang will likely have no qualms about selling its technology.

Some, however, see proliferation as a card the North might be willing to bargain away, provided it can achieve a satisfactory deal with Washington.

"North Korea wants to normalize their relations with the U.S. while they keep their nuclear weapons," said Kim Tae-woo, vice president of the Korea Institute for Defense Analyses. "North Korea will promise not to proliferate" if it can achieve that, he said.

For Washington, that is unlikely to be acceptable. The United States, besides vocally condemning North Korea's nuclear tests, has consistently demanded that the country verifiably abandon its nuclear programs if it wants formal relations.

Given the growing chasm over its nuclear program — North Korea said last month it was pulling out of six-nation talks aimed at its denuclearization after the U.N. Security Council condemned its April rocket launch — and the North's increasingly strident tone, pessimism is growing for any quick end to tensions.

"The hawks tend to be in the drivers seat and I think that's the case in Pyongyang," said the ICG's Pinkston. "The prospects are quite bleak."