North Korea has warned South Korea and the US mainland against "indiscriminate" nuclear strikes as the two allies start large-scale joint military drills on Monday.
The threat to accomplish what it called as a "pre-emptive nuclear strike of justice" was made in a statement by the North's powerful National Defence Commission, referring to the Supreme Command of the Korean People's Army.
It came just days after leader Kim Jong-un directed the country's nuclear arsenal to be put on standby for use "at any moment", in response to new UN sanctions forced over the North's fourth nuclear test in January and last month's long-range rocket launch.
While the North is known to have a small stock of nuclear warheads, experts are divided in their opinion about its ability to scale them on a working missile delivery system.
The National Defence Commission called the annual South Korea-US military exercises as "undisguised nuclear war drills" that jeopardized the North's national sovereignty, and promised an all-out offensive in reaction to "even the slightest military action."
Despite a couple of successful long-range rocket launches, North Korea is believed to be years behind developing a real intercontinental ballistic missile that can reach the US mainland.
This year's drills are known as Key Resolve and Foal Eagle.
Details of the drills have not been revealed, but South Korean Defence Minister Han Min-koo said last month the drills would be the largest in terms of troop size and military assets. Tensions have increased on the Korean peninsula since the North's nuclear test on January 6 and February's rocket launch, which was seen as a camouflaged missile test.
A UN Security Council resolution adopted last week enlisted the toughest sanctions imposed on Pyongyang regarding its nuclear weapons programme and will put significant economic pressure on Kim's regime.