US President Joe Biden arrived in Japan on Sunday after finishing his three-day trip to South Korea, where he visited the Korean Air and Space Operations Center at the US Air Force Base in Osan.

The center south of Seoul is tasked with commanding all aerospace operations by the US and South Korean militaries in the event of any contingency on the Korean Peninsula. South Korean media said Biden was the first US president to visit the center.

Biden said stability is indispensable not only for the Korean Peninsula but for the world.

South Korean President Yoon Suk-yeol told the forces that the center symbolizes the bilateral alliance. He called it a crucial place where the two countries jointly deal with North Korea's nuclear and missile threats, which are growing more sophisticated.

Observers say the US and South Korea were apparently trying to signal Seoul's readiness to respond to Pyongyang's missile threats.

Earlier on Sunday, Biden brushed aside questions about any possible provocation by North Korea, saying, "We are prepared for anything North Korea does."