President Park Geun-hye and her U.S. counterpart Barack Obama visited the Combined Forces Command in Yongsan, Seoul on Saturday.
They were briefed by Gen. Curtis Scaparrotti, commander of the U.S. Forces Korea.
In a speech, Park said urged the CFC officers to maintain a strong deterrence based on a firm combined defense readiness, so that North Korea does not dare to launch any further provocations.
"We go together," she added in English, apparently alluding to the historic nature of the first visit of the presidents from both sides since the command was set up in 1978.
Obama wrote the same phrase in the guest book.
Addressing about 1,500 U.S. military personnel and their families at the U.S. Army Garrison at Yongsan he then repeated it in both Korean and English.
"We will not hesitate to use our military might to defend our allies and our way of life," he added.