The U.S. and South Korean navies began war games Monday ahead of the anticipated arrival of the aircraft carrier USS Ronald Reagan.
While the military stressed the joint drills are routine, tensions are high as North Korea has shown faster-than-expected progress in its weapons programs, including launching missiles from a submarine.
The exercises began on the same day that North Korea celebrated the 71st founding of its ruling Workers’ Party, prompting speculation that it may stage another nuclear or missile test since it often links provocations to high-profile events.
South Korea’s military was on high alert, with an official saying the North could carry out another nuclear test at its leadership’s will. Recent satellite photos have shown activity at all three tunnels at the North’s underground test site.