South Korea and the United States agreed on Thursday on "swift punitive measures" against North Korea in the event of more provocation, although the United States signaled sanctions and diplomatic pressure were its priorities for now.
As a standoff escalated over North Korea's nuclear weapons and long-range ballistic missiles, South Korea said the deployment of a US anti-missile defense system was moving ahead effectively a day after angry protests against the battery and fierce opposition to it from China.
"The two sides pledged that in the event of additional strategic provocation by the North to swiftly take punitive measures including a new UN Security Council resolution that are unbearable for the North," the South's presidential office said after its national security adviser, Kim Kwan-jin, held a phone call with his US counterpart, HR McMaster.
The United States and North Korea have been stepping up warnings to each other in recent weeks over North Korea's development of nuclear weapons and missiles in defiance of U.N. resolutions.
North Korea's nuclear and missile threat is perhaps the most serious security challenge confronting US President Donald Trump. He has vowed to stop it from being able to hit the United States with a nuclear missile.
Though it has warned "all options are on the table", Trump's administration said on Wednesday it aimed to push North Korea into dismantling its weapons programs through tougher sanctions and diplomatic pressure, and it remained open to talks.
Secretary of State Rex Tillerson, Defense Secretary Jim Mattis and Director of National Intelligence Dan Coats described North Korea as "an urgent national security threat and top foreign policy priority".
The US signal of a willingness to exhaust non-military avenues came as the USS Carl Vinson aircraft carrier group approached Korean waters, where it will join the USS Michigan nuclear submarine.