In a statement on state-run television, Pyongyang said no radiation was leaked in the blast. The official Korean Central News Agency said the detonation of a nuclear warhead showed the regime had the ability to attach atomic weapons to rockets.
“The standardization of the nuclear warhead will enable the DPRK to produce at will and as many as it wants a variety of smaller, lighter and diversified nuclear warheads of higher strike power,” KCNA said, using the acronym for North Korea. “This has definitely put on a higher level the DPRK’s technology of mounting nuclear warheads on ballistic rockets.”
South Korean President Park Geun Hye condemned the test -- calling it an action of “maniacal recklessness” -- and warned Kim Jong Un’s moves would lead to North Korea’s self-destruction. The blast set off an artificial earthquake around 9:30am Seoul time, with the defense ministry saying the explosion was 10 kilotons. The United States Geological Survey put the quake magnitude at 5.3.
The miniaturization of the warhead, if true, would be a major leap for North Korea’s nuclear ambitions. North Korea said after its third test in 2013 it had created nuclear missiles capable of reaching the U.S., but produced little proof, drawing skepticism from arms experts. In March it unveiled images of what it called a miniaturized warhead.
Pyongyang said after its January test it had detonated a hydrogen bomb for the first time. That was never verified and some nuclear experts and the U.S. cast doubt on the claim.
Korean stocks and the won fell Friday -- with the Kospi Index down 1.3 percent -- though analysts said the reaction was somewhat muted. The yen rose.
Chief Cabinet Secretary Yoshihide Suga said North Korea’s actions were a threat to Japan and the country would consider further sanctions. U.S. President Barack Obama spoke with Park and with Japanese Prime Minister Shinzo Abe. South Korea’s Yonhap news agency said the United Nations Security Council would meet later Friday.
China, which pushed back against some proposed sanctions after North Korea’s last test in January, said it called on Pyongyang to curb its nuclear plans. Foreign Ministry spokeswoman Hua Chunying said China was firmly opposed to the test and officials would speak to counterparts at the North Korean embassy in Beijing.
The test comes a day after Obama left Asia following his swansong trip as leader. His visit included a clutch of global summits in China -- where he attended a G-20 meeting hosted by President Xi Jinping -- and Laos. During those meetings he and the leaders of Japan and South Korea urged stronger action to curb Kim’s nuclear ambitions.
North Korea has been seeking more miniaturized capability, said Lim Eul Chul, a professor of international political economy at Kyungnam University in Seoul. “The smaller the warhead, the further the weapon can fly,” Lime said. “The results would have to come out, but for now I see that North Korea’s nuclear technology has come to a stage where it’s right before being arranged for combat.”
Han Yong-Sup, a professor at the Korea National Defense University and former adviser to the National Security Council standing committee and foreign ministry, said he believed North Korea had achieved miniaturization. “They are at the stage of giving final touches to make it fit onto” intercontinental or submarine launched ballistic missiles, he said. “They probably can already fit on Rodong missiles.”
“I personally thought it would conduct the test in December. To advance the date means it is trying to show they have everything ready before the next U.S. administration starts its term.”
North Korea test-fired a trio of ballistic missiles that landed within a few hundred kilometers of Japan’s coast earlier this week. The regime, which has repeatedly flouted Security Council resolutions barring its ballistic missile activities, has conducted at least 22 launches this year, according to U.S. officials.
China has done more on sanctions against North Korea than previous rounds of penalties but could “tighten up” in prodding Kim, Obama told reporters on Thursday in Laos. Obama said he had told Xi that China needs to “work with us more effectively” to rein Kim in.
Tensions in North Asia have also been running high over a plan to deploy a U.S. missile defense system known as Thaad in South Korea. The Chinese have protested that move, which U.S. officials insist is only intended to protect South Korea. Russia has also objected.
The latest blast probably reflects North Korean efforts to cause further fractures between the U.S. and China over Thaad, said Lee Woo Young, a professor at the University of North Korean Studies in Seoul. “The test would show North Korea’s willingness to break the power balance in the East Asia region.”
Obama said he noted Xi’s objection to Thaad and that the U.S. is not looking for a diplomatic tussle over the missile shield. Still, he said, “we cannot have a situation where we’re unable to defend ourselves or our treaty allies against increasingly provocative behavior."
“They need to work with us more effectively to change Pyongyang’s behavior,” Obama said, referring to China.
The big question for the international community is whether it can match its condemnation of North Korea with action, according to Scott Snyder, a senior fellow for Korea studies at the Council on Foreign Relations.
“A second question is whether the United States and China can set aside strategic mistrust sufficiently to coordinate a set of actions that would make clear that Kim Jong Un’s current path is unacceptable and force him to turn around and accept denuclearization."