Lee Jin-Man/Associated Press
A South Korean watched news reporting about a possible nuclear test conducted by North Korea on a TV screen in Seoul on Tuesday.
WASHINGTON — North Korea appeared to conduct its third, and probably largest, nuclear test on Tuesday, according to American and Asian officials, posing a new challenge for the Obama administration in its effort to keep the country from becoming a full-fledged nuclear power.
While North Korea’s official news outlets were silent about the test, many nations detected seismic activity centered near the same location where the North conducted tests in 2006 and 2009. The United States Geological Survey said it was only a kilometer underground, an indication consistent with a nuclear blast. And in Vienna, the organization that monitors the Comprehensive Nuclear Test Ban Treaty said that tremor had “clear explosionlike characteristics.”
Preliminary estimates suggested a test far larger than the previous two conducted by the North, though probably less powerful than the first bomb the United States dropped on Japan, in Hiroshima, in 1945.
If confirmed, the test would be the first under the country’s new leader, Kim Jong-un, and an open act of defiance to the Chinese, who urged the young leader not to risk open confrontation by setting off the weapon. In the past few days a Chinese newspaper that is often reflective of the government’s thinking said the North must “pay a heavy price” if it proceeded with the test. But it was unclear how China would act at the United Nations Security Council, which was heading into emergency session as news of the suspected blast played out.
The Obama administration has already threatened to take additional action to penalize the North if it conducts a test, through the United Nations. But the fact is that there are few sanctions left to apply against the most unpredictable country in Asia. The only penalty that would truly hurt the North would be a cutoff of oil and other aid from China. And until now, despite issuing warnings, the Chinese have feared instability and chaos in the North more than its growing nuclear and missile capability, and the Chinese leadership has refused to participate in sanctions.
Mr. Kim, believed to be about 29, appears to be betting that even a third test would not change the Chinese calculus.
The apparent test set off a scramble among Washington’s Asian allies to assess what the North Koreans had done.
The United States sent aloft aircraft equipped with delicate sensors that may, depending on the winds, be able to determine whether it was a plutonium or uranium weapon. The Japanese defense minister, Itsunori Onodera, said Japan had ordered the dispatch of an Air Self-Defense Force jet to monitor for radioactivity in Japanese airspace.
Japan’s new prime minister, Shinzo Abe, told Parliament that “based on precedents, Japan believes that this quake was triggered by a North Korean nuclear test,” and said the country was considering “its own actions, including sanctions, to resolve this and other issues.”
But the threat may be largely empty, because trade is limited and the United States and its allies have refrained from a naval blockade of North Korea or other steps that could revive open conflict, which has been avoided on the Korean Peninsula since an armistice was declared 60 years ago.
It may take days or weeks to determine if the test, if that is what it proves to be, was successful. American officials will also be looking for signs of whether the North, for the first time, conducted a test of a uranium weapon, based on a uranium enrichment capability it has been pursuing for a decade. The past two tests used plutonium, reprocessed from one of the country’s now-defunct nuclear reactors. While the country has only enough plutonium for a half-dozen or so bombs, it can produce enriched uranium well into the future.
No country is more interested in the results of the North’s nuclear program, or the Western reaction, than Iran, which is pursuing its own uranium enrichment program. The two countries have long cooperated on missile technology, and many intelligence officials believe they share nuclear knowledge as well, though so far there is no hard evidence.
