North Korea's military says it artillery forces are at their highest-level combat posture in its latest threat to attack South Korea and the US.
Seoul said it is not seeing any suspicious North Korean military activity, and analysts say a direct North Korean attack is extremely unlikely, especially during joint US-South Korean military drills that end on April 30.
But the rival Koreas have had several bloody naval skirmishes in disputed Yellow Sea waters and there is some worry among analysts about a provocation after the drills.
Observers said Tuesday's statement by the North Korean army's Supreme Command and other recent bellicose language is partly meant to strengthen internal loyalty to leader Kim Jong Un.
Pyongyang is angry over recent UN sanctions over its nuclear test and says Washington and Seoul plan to invade.