helped to bring Mr. Trump and Mr. Kim together for two summits. But after the second, in 2019, abruptly ended without an agreement on American sanctions relief or the pace of North Korean disarmament, Mr. Moon struggled to regain his relevance in negotiations. Last June, North Korea blew up the joint inter-Korean liaison office on its side of the border, the first of a series of actions that threatened to reverse a fragile détente.

diatribe issued hours after the senior American envoys landed in Tokyo earlier this week, North Korea warned the Biden administration to “refrain from causing a stink.”

vowed to further advance his country’s nuclear capabilities, declaring that it would build new solid-fuel I.C.B.M.s and make its nuclear warheads lighter and more precise.

Analysts said Pyongyang was closely following this week’s trips by Mr. Blinken and Mr. Austin to Tokyo and Seoul for clues to the Biden administration’s approach. It is expected that North Korea will decide after watching Washington whether to resume weapons tests and create a new cycle of tensions to gain leverage.

a fix ever since the North Korea-United States talks broke down.”

Mr. Blinken said the American posture toward North Korea would include a mix of regional pressure options and the potential for future diplomacy when the Biden administration’s current policy review is concluded, as soon as next month.

Mr. Aum, the North Korea expert at the U.S. Institute of Peace, said that the policy could include plying China to do more to rein in North Korea, potentially by deploying additional weapons systems in the region or conducting larger military exercises with South Korea — both of which would irritate Beijing.

China has largely urged North Korea and the United States to resolve the impasse themselves, although it has called for sanctions relief and a pause of American military exercises with Seoul in exchange for Pyongyang freezing its nuclear and missile tests.

“All parties should work together to sustain peace and stability on the Korean Peninsula,” a spokesman for China’s Ministry of Foreign Affairs, Zhao Lijian, said this week. “China will continue to play a constructive role in this process.”

Steven Lee Myers and John Ismay contributed reporting from Seoul.

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