Washington regards North Korea's accelerated push to acquire a nuclear-armed missile capable of threatening the United States and other countries as a "clear and present danger," U.S. Defense Secretary Jim Mattis says.
Speaking on June 3 at an international security conference in Singapore, Mattis called North Korea an "urgent military threat."
"We're working diplomatically, economically, we're trying to exhaust all possible alternatives to avert this race for a nuclear weapon in violation of...the United Nations' restrictions on North Korea's activities," he said.
"We want to stop this. We consider it urgent," he added.
However, during his address to the Shangri-La Dialogue, sponsored by the International Institute for Strategic Studies, Mattis said that U.S. President Donald Trump's administration was encouraged by China's renewed commitment to working with Washington and others to rid North Korea of its nuclear weapons.
China, North Korea's closest ally, blocked tough new sanctions against North Korea that the United States pushed in the UN Security Council on June 2.
However, the Security Council did vote unanimously to add 15 individuals and four entities linked to the North's nuclear and missile programs to a UN sanctions blacklist.
Mattis also delivered sharp criticism of what he called China's disregard for international law by its "indisputable militarization" of artificial islands in disputed areas of the South China Sea.
"We cannot and will not accept unilateral, coercive changes to the status quo" in the South China Sea, Mattis said.
But Mattis voiced hope for cooperation and peace in the Asia-Pacific region.
"While competition between the United States and China, the world's two largest economies, is bound to occur, conflict is not inevitable," he said. "Our two countries can and do cooperate for mutual benefit. We will pledge to work closely with China where we share common cause."
Washington has some 28,500 troops permanently based in South Korea, a defense-treaty ally. In his speech, Mattis said the United States will stick to its treaty commitments to South Korea.
"While the North Korean regime has a long record of murder of diplomats, of kidnapping, killing of sailors, and criminal activity, its nuclear-weapons program is maturing as a threat to all," Mattis said. "As a matter of national security, the United States regards the threat from North Korea as a clear and present danger."
With reporting by AP, BBC, and AFP