In a statement released on Tuesday the North Korean army warned that it "reserves the right to undertake a pre-emptive action for self-defense against the enemy at a crucial time it deems necessary to defend itself."
The statement comes amid continued tensions over the secretive regime's military intentions and concerns that it may be preparing to test a nuclear weapon.
Last month North Korea launched a series of missile tests, including of its long range Taepondong 2 missile.
Although the Taepodong missile failed shortly after launch, the tests were condemned as provocative by countries such as the US and Japan.
North and South Korea remain technically at war never having signed a peace treaty formally ending the 1950-53 Korean War.
Instead the two countries have been engaged in an uneasy stand-off for more than 50 years under a UN-monitored armistice.
North Korea frequently issues warnings that the Korean peninsula stands on the brink of a renewed war.
Earlier it had said that the annual joint South Korean-US exercises, involving some 17,000 troops, would be seen as a declaration of war if they went ahead.