President Barack Obama said on Saturday the United States did not use its military might to "impose things" on others, but that it would use that might if necessary to defend South Korea from any attack by the reclusive North.
The North warned last month it would not rule out a "new form" of atomic test after the U.N. Security Council condemned Pyongyang's launch of a mid-range ballistic missile into the sea east of the Korean peninsula.
Obama and South Korean President Park Geun-hye presented a united front against North Korea at a joint news conference following their summit on Friday, warning that they would respond firmly to any "provocations" by Pyongyang which routinely threatens the United States and South Korea with destruction.
"We don't use our military might to impose these things on others, but we will not hesitate to use our military might to defend our allies and our way of life," Obama told cheering U.S. forces at the Yongsan garrison on a sunny spring morning.
"So like all nations on Earth, North Korea and its people have a choice. They can choose to continue down a lonely road of isolation, or they can choose to join the rest of the world and seek a future of greater opportunity, and greater security, and greater respect - a future that already exists for the citizens on the southern end of the Korean peninsula."
North Korea is already subject to U.N. sanctions over its previous three atomic tests.