UNITED NATIONS—Japanese Prime Minister Shinzo Abe said North Korea’s nuclear threat has reached a dimension that demands stepped up efforts, while the No. 2 official of Pyongyang’s lone ally—China—offered a more measured assessment and urged dialogue.
Mr. Abe and Chinese Premier Li Keqiang addressed world leaders at the United Nations General Assembly on Wednesday, nearly two weeks after North Korea conducted its fifth nuclear test in a decade.
World powers are grappling with how to confront dictator Kim Jong Un’s increasingly aggressive behavior. The U.S. sees China as key to reining in Pyongyang, and senior American officials have repeatedly said that China must do more to pressure Mr. Kim both financially and diplomatically. Beijing has historically resisted taking steps that could destabilize its neighbor.
Mr. Abe called on world powers to “concentrate our strengths and thwart North Korea’s plans.”
“There is no alternative but to say that the threat has now reached a dimension altogether different from what has transpired until now,” Mr. Abe said in his speech. “We must therefore respond to this in a manner entirely distinct from our responses thus far.”
Mr. Li, Beijing’s top representative at this year’s summit, didn’t sound alarms and reiterated previous calls for international dialogue.
“We should remain committed to denuclearization of the Korean Peninsula, uphold peace and stability on the Korean Peninsula and seek consultation and dialogue-based solutions so as to maintain the international nuclear nonproliferation regime,” Mr. Li said, giving the controversial security challenge only a brief mention in his 20-minute address.
Earlier this week, The Wall Street Journal reported that the U.S. and China are targeting the finances of a Chinese conglomerate headed by a Communist Party member who the Obama administration believes has played a key role in helping Pyongyang’s nuclear program.
U.N. diplomats are also considering further sanctions on North Korea.
President Barack Obama met with Mr. Li on Monday on the sidelines of the summit and pledged to step up coordination to confront Pyongyang’s nuclear program through the U.N. and through law-enforcement channels.
Mr. Li and Mr. Abe also addressed another regional hot spot, the South China Sea. Neither named the body of water where China and several southeast Asian countries have a long-running territorial dispute.
“China also maintains that disputes concerning territory and maritime rights and interests should be resolved through dialogue and negotiation,” Mr. Li said. “We need to expand common ground while shelving differences and make continuous contributions to regional peace and stability.”
China’s claims are marked by the so-called nine-dash line that was rejected by an international tribunal this summer. China has said it won’t abide by the decision.
Mr. Abe urged countries to observe international law.
“Should there be disputes, the international community must adhere strictly to the principles that states shall make their claims based on international law, they shall not use force or coercion in trying to drive their claims, and they shall seek to settle disputes by peaceful means,” Mr. Abe said.
—Valentina Pop contributed to this article.
Write to Felicia Schwartz at Felicia.Schwartz@wsj.com
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