SEOUL, South Korea (AP) — South Korea’s president said Tuesday a solid alliance with the U.S. strengthens the foundation of national security, as many South Koreans were baffled and concerned about U.S. President Donald Trump’s abrupt order to “substantially reduce” joint military exercises.

Trump made the surprise announcement in a social media post just before U.S. and South Korean soldiers began Monday’s annual Ulchi Freedom Shield exercises, which are largely designed to sharpen readiness against North Korean threats.