U.S. President Joe Biden and his South Korean counterpart Yoon Suk-yeol visited an air defense headquarters near Seoul on Sunday to show North Korea their willingness to respond to “nuclear and missile provocations,” according to Yoon’s office.

The inside of the Korea Air and Space Operations Center (KAOC) at Osan Air Base was first revealed to the public when Biden and Yoon delivered remarks at the center on the third and final day of Biden’s first presidential visit to the Korean Peninsula.