The North has in recent months been seen upping activity at its Punggye-ri nuclear test site. It formally declared an intention to conduct its third test after being slapped with strengthened U.N. Security Council sanctions last month for launching a long-range rocket in December. That set off a wave of educated guessing on when the device would actually be detonated.
South Korean analysts suspect it will happen before the Feb. 16 birthday of former North Korean leader Kim Jong Il, who died in December 2011 and was replaced by his son, Kim Jong Un. It could also be timed to President Obama's next State of the Union address on Tuesday, according to professor Yang Moo-jin of the University of North Korean Studies.
"The nuclear agenda of the North is about pressing the United States. Hence, it would make sense for Kim Jong Un to carry out a nuclear test in time with the State of the Union address," Yang said.
"Mid-February is the most plausible time, in particular ahead of Kim Jong Il's birthday," said Chang Yong-seok of Seoul National University. "In light of its track record, Presidents Day on Feb. 18 is another possibility."
Experts have also said the test could involve multiple devices and that highly enriched uranium might be used. Previous devices incorporated plutonium.
China is pressing its neighboring ally not to follow through on its threat of a follow-up to its 2006 and 2009 nuclear trials, Arirang reported. It has quietly threatened to halt key assistance to the North, among other strategies for heading off the test, according to the report.
South Korea would quickly request that the Security Council meet in the wake of a North Korean test to discuss sanctions or other responses, Kyodo News reported.
Japan could institute its own new economic penalties against the North should the test occur, the Xinhua News Agency reported on Thursday.