A statement by the head of the U.N. Comprehensive Test Ban Treaty Organization, a Vienna, Austria-based organization that monitors compliance with the bedrock international nuclear non-proliferation accord through globe-spanning networks of seismographs and other sensors, said the "unusual seismic event" in North Korea "shows explosion-like characteristics."

"Its location is roughly congruent with the 2006 and 2009 (North Korean) nuclear tests," CTBTO Director General Tibor Toth said. "For now, further data and analysis are necessary to establish what kind of event this is. If confirmed as a nuclear test, this act would constitute a clear threat to international peace and security, and challenges efforts made to strengthen global nuclear disarmament and non-proliferation, in particular by ending nuclear testing.”

North Korea’s 2006 test was confirmed to have involved a device that used plutonium reprocessed from the used fuel rods of a shuttered nuclear reactor. U.S. intelligence officials determined from radioactive debris found in air samples that the yield was less than a kiloton.

A 2009 underground test blast is believed to also have been produced by a plutonium device, although there has been no confirmation, said Acton. It is believed to have been almost as powerful as the Nagasaki bomb, with the Russian Defense Ministry estimating the yield at 20 kilotons.

Acton said that if the latest suspected explosion “vented” radioactive material into the atmosphere, analyses of samples collected by specialized aircraft believed to be operated by the United States and other countries will determine if the device was fueled by highly enriched uranium.

“North Korea has only a limited amount of plutonium,” Acton said. “If this test turns out to be highly enriched uranium, that means they have mastered highly enriched uranium production and that means they can make their arsenal much bigger relatively quickly.”

In December, North Korea defied United Nations’ sanctions by launching a satellite that was seen as a thinly disguised test of ballistic missile technology. North Korea is not thought to have the ability to place a nuclear warhead on top of a missile capable of reaching the United States, but the twin tracks of developing longer-range missiles and conducting further nuclear tests raise the question of whether it’s working in that direction.

Tuesday’s nuclear test fell in line with threats made last month by North Korea’s National Defense Commission to do just that. The commission is headed by the nation’s young leader, Kim Jong Un, who’s thought to be about 30-years-old.

The test will almost certainly strain relations with North Korea’s largest backer, China, which has signaled repeatedly that it has tired of diplomatic headaches brought on by the secretive nation. The Global Times newspaper in Beijing, which while not an official mouthpiece of the Chinese Communist Party is state-controlled, ran a strongly-worded editorial earlier this month saying that, “if North Korea insists on a third nuclear test despite attempts to dissuade it, it must pay a heavy price. The assistance it will be able to receive from China should be reduced.”

Because of the strategic importance Chinese officials see in maintaining relations with North Korea – maintaining a buffer between China and U.S. troops stationed in South Korea, and avoiding the chaos of a fallen North Korea spilling over its borders – Beijing is not likely to be anywhere close to pulling the plug on aid and support.

But frustrations with Pyongyang in China, which is currently in the middle of Chinese New Year celebrations, might well lend support to stronger sanctions by the U.N. Security Council.