Top South Korean, U.S. and Japanese military officers urged North Korea to cease all unlawful activities that threaten regional security, as the three nations flew advanced warplanes for a joint exercise in a show of force against the North.

South Korea, Japan and the United States conducted a joint air drill on Friday involving a U.S. B-52 strategic bomber and fighter jets of the three allies over international waters, the South's defence ministry said.

The Joint Chiefs of Staff of South Korea, the United States and Japan pledged to continue working together toward the complete denuclearization of North Korea, amid discussions about a possible shift in the role of U.