North Korea has threatened the US and South Korea with a “pre-emptive nuclear strike of justice” after the two countries started huge drills.
Pyongyang claims the exercises, which happen every year, are rehearsals for an of North Korea.
But Washington and Seoul maintain the war games are purely defensive.
The North’s powerful National Defence Commission threatened strikes against targets in South Korea, US bases in the Pacific and the US mainland, saying its enemies “are working with bloodshot eyes to infringe upon the dignity, sovereignty and vital rights” of North Korea.
“If we push the buttons to annihilate the enemies even right now, all bases of provocations will be reduced to seas in flames and ashes in a moment,” the statement said.
South Korean Defence Ministry spokesman Moon Sang Gyun said Pyongyang must refrain from a “rash act that brings destruction upon itself”.
This year’s drills will be the largest ever held, and will involve 300,000 South Korean and 17,000 US .
The two countries will work on drills for precision attacks on North Korea’s leadership and its nuclear and missile arsenal in the event of war, according to South Korean news agency Yonhap, which cited sources.
There remains considerable debate about whether North Korea is capable of the kind of strikes it regularly threatens.
Pyongyang staged its fourth nuclear test in January, but many experts say its arsenal still may only be made up of crude weapons.
It is not known if the North has mastered the miniaturisation process required to mount bombs on long-range missiles, and there are doubts about whether they possess a reliable missile that could hit the US mainland.
Relations between North Korea and the West worsened following its latest nuclear test and a long-range rocket launch last month that outsiders say was a test of banned ballistic missile technology.
The recently hit the country with harsh new sanctions, and South Korea has said it will announce new unilateral sanctions on Tuesday.