U.S. President Barack Obama warned North Korea of the consequences of a possible fourth nuclear test on Saturday while visiting the American military installation in Seoul.

The president paid a visit to the Yongsan Garrison in the nation’s capital with his South Korean counterpart, Park Geun-hye. It was the first time for leaders of the two countries to visit the joint U.S.-South Korea command together since its establishment in 1978.

The two presidents were met by U.S. Army General Curtis Scaparrotti, commander of the joint U.S.-South Korea command, who briefed the presidents and told them that his team “works very