North Korea conducted its second nuclear test May 25, prompting international condemnation for violating UN demands and raising tensions in the region. The test comes a month after North Korea declared that it would no longer participate in multilateral talks on its denuclearization and would carry out nuclear and missile tests to strengthen its deterrent capability. (See ACT, May 2009.) After the test, Pyongyang's official Korean Central News Agency (KCNA) struck a similar note, saying the blast was "part of the measures to bolster up [North Korea's] nuclear deterrent for self-defense."
U.S. statements responding to the test focused particularly on the consequence of Pyongyang's increasing isolation following its actions and on Washington's intention to coordinate a response both within the UN Security Council and with other countries in the region previously involved in six-way negotiations with North Korea. The morning after the test, President Barack Obama said that, in response to the nuclear test, the United States and its four partners in the regional talks-China, Japan, Russia, and South Korea-"have all come to the same conclusion: North Korea will not find security and respect through threats and illegal weapons."
Moscow and Beijing issued their own condemnatory statements immediately after the test. Chinese Foreign Ministry spokesman Ma Zhaoxu said May 26 that China "resolutely opposed" the test and that, in carrying it out, North Korea had "ignored [the] universal opposition of the international community."
Russia said the test undermined the nuclear nonproliferation regime, as well as regional security. Russian officials expressed particular concern over the continued development of North Korea's nonconventional military capabilities. "Particularly disturbing is the fact that North Korea's nuclear program is carried out in conjunction with the development of missile technologies," Presidential Press Secretary Natalia Timakova said May 27.
Following a May 26 emergency meeting called by Japan, the UN Security Council responded to the test by issuing a statement declaring it to be a "clear violation" of Resolution 1718. Council members also indicated that they would begin work "immediately" on a new resolution.
Resolution 1718, which the council adopted in 2006 following North Korea's explosion of a nuclear device earlier that year, prohibited Pyongyang from carrying out any further nuclear tests.
The United States will be seeking a new Security Council resolution "with teeth," Susan Rice, U.S. permanent representative to the United Nations, said during a May 26 press briefing. "Those teeth could take various different forms. There are economic levers-there are other levers that we might pursue," she added.
Although China strongly condemned the test, it is unclear how far North Korea's closest ally and most significant benefactor is willing to go in imposing penalties on Pyongyang for violating the council's demands. In his May 26 comments, Ma said that "relevant parties" must respond to the launch in a "coolheaded and appropriate way." China used similar language in April when it agreed to a stern Security Council statement responding to North Korea's rocket launch but opposed a more legally binding resolution. (See ACT, May 2009.)
Current and former U.S. officials and politicians seemed to be hopeful of China's cooperation in crafting a strong response. White House Press Secretary Robert Gibbs told reporters May 28 that Beijing has been "very helpful" in discussions at the UN on North Korea.
Speaking to reporters in Beijing following meetings with senior Chinese officials there, Senate Foreign Relations Committee Chairman John Kerry (D-Mass.) said that Foreign Minister Yang Jiechi "agreed with us that North Korea's actions were wrong and that there need to be consequences."
According to Dennis Wilder, former senior National Security Council director for East Asian affairs, "We are seeing the Chinese beginning to move to a stronger position on this nuclear test." Speaking to a Brookings Institution audience May 27, Wilder said China has used its political and economic leverage over North Korea in the past with positive results, including in 2003 to encourage Pyongyang to join in six-party talks and in 2006 in response to the first nuclear test.
South Korea Joins PSI
The day following the test, South Korea announced that it would formally join the Proliferation Security Initiative (PSI), a U.S.-led effort that focuses on interdiction and coordinated information-sharing to prevent the proliferation of nonconventional weapons and materials. Seoul previously was an observer to the informal group, which comprises about 96 participants.
Outlining Seoul's rationale for joining the initiative, Foreign Minister Yu Myung-hwan told the South Korean National Assembly May 26 that the North Korean nuclear test "proves the threats of proliferation of dangerous weapons have increased" and that endorsing the PSI was Seoul's "duty as a member of the international community."
A South Korean diplomat told Arms Control Today May 27 that although Seoul is prepared to inspect and interdict suspect shipments, participation in the PSI is primarily intended to deter North Korea from using the South's territory to proliferate or acquire sensitive technologies.
South Korea was already considering joining the PSI following North Korea's rocket launch last month but delayed making an announcement because of apparent divisions within the South Korean government and concerns about North Korea's reaction. (See ACT, May 2009.)
Pyongyang had previously stated that Seoul's participation in the PSI would constitute an act of war. Following through on this threat, KCNA said May 27 that the North Korean army "will not be bound to the  Armistice Agreement any longer" and that North Korea would "deal a decisive and merciless retaliatory blow" in response to the inspection of its ships by South Korea.
The Armistice Agreement ended hostilities following the Korean War. A formal peace agreement has never been concluded.
Test Analysis Under Way
Early estimates indicate that the test was at least more successful than North Korea's first nuclear detonation in 2006. Siegfried Hecker, former director of Los Alamos National Laboratory, estimated May 26 that the yield was between two and four kilotons.
In comparison, North Korea's 2006 test was estimated to be about 0.5 kilotons and at best a partial success. (See ACT, November 2006.) Prior to that test, Pyongyang reportedly informed Beijing that it expected a yield of four kilotons. It is unclear what yield North Korea intended to achieve with the May test.
Preliminary estimates of the yield of the test have been based solely on seismic data generated by the shockwaves that emanated from the test site, located a few kilometers from the 2006 test near the village of P'unggye. According to a May 25 press release by the Comprehensive Test Ban Treaty Organization, analysis of the noble gases released from the underground explosion will proceed in the coming days.