Kim Jong Un Calls for Better Bombs as Korean Tensions Remain High

North Korean leader Kim Jong Un called on his scientists to do more to boost the country’s arsenal after the regime conducted its fourth nuclear test last week in defiance of neighbors including China and South Korea.

Speaking to the scientists responsible for building what North Korea said was a hydrogen bomb, Kim said it was his “expectation and conviction” that they would advance their research, the official Korean Central News Agency said Monday. Kim has said the nuclear program is defensive and designed to prevent a U.S.-led invasion.

Kim’s comments come as the United States and South Korea seek international support to punish the isolated nation for the test and pressure it to halt its nuclear program. The U.S. on Sunday sent a B-52 bomber on a low-level flight south of Seoul, while South Korea has restarted propaganda broadcasts across its heavily armed northern border. The loudspeaker bursts risk pushing South Korea and North Korea “toward the brink of war,” North Korean official Kim Ki Nam said on Friday, Yonhap reported.

“North Korea has every political and technical reason to test nuclear devices and missiles,” said Duyeon Kim, a Seoul-based non-resident associate in the Nuclear Policy Program and Asia Program at the Carnegie Endowment for International Peace. “We know they will continue doing it, so the real question is ‘what will we do about it?’”

North Korea launched a long-range rocket before each of its previous three nuclear tests, which resulted in a tightening of international sanctions. But trade bans on arms and luxury items have failed to convince it to return to disarmament talks that broke down in 2009, leading it to revive the production of nuclear devices.

The U.S. and South Korea are struggling to get backing for a united response from China, which is North Korea’s main ally. South Korean nuclear negotiator Hwang Joon-kook will meet with his Chinese counterpart Wu Dawei in China on Thursday to discuss the issue, Seoul’s Foreign Ministry said. Hwang will separately meet with his Japanese and U.S. counterparts in Seoul on Wednesday.

Chinese Foreign Minister Wang Yi told his South Korean counterpart Yun Byung-se by phone Friday that efforts should be made to restart talks to end North Korea’s nuclear program, according to a text message from South Korea’s foreign ministry. Secretary of State John Kerry on Thursday urged China to support a more aggressive approach with Pyongyang, saying its North Korea policy had been a failure.

In an editorial, China’s official Global Times newspaper blamed the “hostile policy” of the U.S. toward North Korea for prompting the nuclear tests.

“China is not the cause and crux of the Korean nuclear issue, nor is it the key to resolving the problem,” Foreign Ministry spokeswoman Hua Chunying said in Beijing on Friday.

Still, the second nuclear test since Kim came to power four years ago may have angered President Xi Jinping, who in October sent a high-ranking envoy to Pyongyang with a handwritten letter seeking deeper cooperation. North Korea, while accepting energy and food aid from China, has spurned Beijing’s efforts to drop its nuclear program and return to talks.

China may be reluctant to crack down hard on North Korea for fear of destabilizing the regime in case it sends millions of refugees across China’s border or leads to an eventual unification with the South, leaving a well-armed U.S. ally on China’s frontier.

The potential for a collapse in North Korea is a bigger threat to South Korea than a direct military confrontation, credit ratings agency Moody’s Investors Service analysts Shirin Mohammadi and Steffen Dyck said in an e-mailed note Monday.

“The North Korean regime has survived for more than 65 years, but internal economic and political strains could eventually lead to a sudden collapse. Such a development is a risk that would pose enormous challenges for South Korea,” they wrote.