The US urged North Korea on Friday to avoid taking any provocative steps following a clash earlier in the week between North and South Korean warships.
Ahead of President Barack Obama's visit to South Korea next week, Pyongyang issued a warning that the South Korean Army will "pay dearly" for the skirmish, and that North Korea will take "merciless military measures" if its self-determined maritime border is threatened.
"We would urge North Korea to refrain from that kind of bellicose rhetoric and, in general, avoid any kind of provocative actions that would further inflame the tension in the region," US State Department spokesman Ian Kelly said.
Kelly would not draw a connection between the latest threats and Obama's visit to Seoul on Thursday. North and South Korean naval vessels exchanged fire on Tuesday, each blaming the other in a sea border dispute. There were no casualties in the incident but both ships were damaged.