SINGAPORE (AP) — North Korea is accelerating its push to acquire a nuclear-armed missile capable of threatening the United States and other nations, and the U.S. regards this as a “clear and present danger,” U.S. Defense Secretary Jim Mattis said today.

Speaking at an international security conference in Singapore, Mattis said the Trump administration is encouraged by China’s renewed commitment to working with the U.S. and others to rid North Korea of its nuclear weapons. He also said he thinks China, which is North Korea’s closest ally, ultimately will see it as a liability.

China blocked tough new sanctions against North Korea the United States pushed in the U.N. Security Council on Friday. 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 U.N. sanctions blacklist.

In his speech to the Shangri-La Dialogue, sponsored by the International Institute for Strategic Studies, Mattis sought to balance his hopeful comments on China with sharp criticism of what he called Beijing’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, he said.