April 23, 2014 3:02 am JST

North Korea stirring up nuclear trouble ahead of Obama visit

KIYOYUKI UCHIYAMA, Nikkei staff writer

SEOUL -- Japan, the U.S. and South Korea are keeping a closer-than-usual eye on North Korea amid signs that it is preparing for a fourth nuclear test.

     With U.S. President Barack Obama kicking off back-to-back visits to Japan and South Korea on Wednesday, Pyongyang may be trying to manufacture a crisis in hopes of starting a dialogue with Washington.

     The North is ready to stage "a surprise nuclear test" as soon as the order is given, a South Korean defense ministry spokesman told reporters Tuesday.

     The ministry has picked up on activity at Punggye-ri, the site of past tests, the spokesperson said.

     North Korea's foreign ministry said late last month that it "would not rule out a new form of nuclear test" to bolster its deterrent. Experts say its options may include a highly enriched uranium weapon, which is easier to build than the plutonium bombs it is known to have; a hydrogen bomb; and a boosted-fission weapon, essentially a single-stage hydrogen bomb.

     "North Korea is likely to do a nuclear test in a risky bid to break its impasse," said Moon Seong-mook, a research fellow at the Korea Research Institute for Strategy. Pyongyang is presumably seeking relief from economic sanctions or an unconditional resumption of six-way talks with the U.S., Japan, South Korea, China and Russia.

     In the past, the North has fired off ballistic missiles as a prelude. It did so last month, suggesting that it actually is readying a test, which some observers say may mark a necessary step in its nuclear weapons development.

     Another motivation could be to key up the populace. Obama's summit Friday with South Korean President Park Geun-hye falls on Military Foundation Day, a North Korean holiday.

     But many think that Pyongyang is simply bluffing. It "would face an inevitable tightening of sanctions by the international community, including China," should it go ahead with a test, said Kim Jung-bong, a professor at Hanzhong University in South Korea.

     Japan is "working to gather and analyze information" on the situation, Foreign Minister Fumio Kishida told reporters. With Obama about to arrive, officials in Tokyo are on edge.

     "North Korea may be trying to deter the president's visit," a defense ministry source speculated, noting that last month's missile launches coincided with Obama's summit with Park and Japanese Prime Minister Shinzo Abe in the Netherlands.