“Ultimately, we believe China will come to recognize North Korea as a strategic liability, not an asset.”

However, Mattis said seeking China’s cooperation on North Korea did not mean Washington would not challenge Beijing’s activities in the South China Sea.

The U.N. Security Council on Friday expanded targeted sanctions against North Korea after its repeated missile tests, adopting the first such resolution agreed by the United States and China since Trump took office.

In another sign of increased pressure on North Korea, Japan’s navy and air force began a three-day military exercise with two U.S. aircraft carriers in the Sea of Japan on Thursday.