Speaking to war veterans on the 69th anniversary of the end of the 1950-53 Korean War, Kim emphasised the country's "thorough readiness" to "deal with any military clash with the United States".
His latest threats come as South Korea and the United States move to ramp up joint military exercises, which have always infuriated the North as Pyongyang considers them rehearsals for invasion.
This week, the US military held live-fire drills using its advanced Apache helicopters stationed in the South for the first time since 2019.
Kim also slammed South Korea's new, hawkish president Yoon Suk-yeol, who took office in May and has vowed to take a tougher stance against Pyongyang -- which includes a plan to mobilise a preemptive strike capability.
"Talking about military action against our nation, which possess absolute weapons that they fear the most, is preposterous and is very dangerous self-destructive action," Kim said of the Yoon administration, which he branded a group of "gangsters".
"Such a dangerous attempt will be immediately punished by our powerful strength and the Yoon Suk Yeol government and his military will be annihilated."
The North has carried out a record-breaking blitz of sanctions-busting weapons tests this year, including firing an intercontinental ballistic missile at full range for the first time since 2017.
Nuclear talks between Pyongyang and Washington have been stalled since a summit between Kim and then-US president Donald Trump in February 2019 broke down over sanctions relief and what the North would be willing to give up in return.
The Kim regime has since rejected Washington and Seoul's repeated offers to resume talks, claiming the United States must first drop its "hostile" policies.
Impoverished Pyongyang has long struggled to feed its people and its economy has been battered by pandemic-led border closures as well as sanctions over its nuclear programmes.
The country has also been battling a massive outbreak of "fever" after it confirmed its first cases of Covid-19 in May.
"Kim's rhetoric inflates external threats to justify his militarily focused and economically struggling regime," said Leif-Eric Easley, a professor at Ewha University in Seoul.
"North Korea's nuclear and missile programs are in violation of international law, but Kim tries to depict his destabilising arms buildup as a righteous effort at self-defence."