However, he left the door open to dialogue with Washington as he concluded a ruling party congress outlining his policy goals for the next five years.
Kim in recent years has sharpened his rhetoric towards Seoul and underscored his rejection of inter-Korean diplomacy.
Experts say that most likely does not presage military clashes, but is intended to advance a broader effort to assert a more forceful regional role backed by Kim's nuclear arsenal and ties with Moscow and Beijing.
The official Korean Central News Agency said Kim also called for developing new weapons systems to bolster his nuclear-armed military, including intercontinental ballistic missiles that could be launched from under water and an expanded arsenal of tactical nuclear weapons targeting South Korea.
He said the country's status as a nuclear weapons state was "permanently cemented", and called for the United States to discard "hostile" policies towards the North if it wanted to resume long-stalled dialogue.
South Korea's unification ministry said it was regrettable that the North continued to define relations as hostile and that Seoul would "patiently" pursue efforts to stabilise peace.
The Workers' Party congress, which began last Thursday in Pyongyang, is the country's most important political event.
KCNA said the North staged a military parade on Wednesday as it wrapped up the congress, which was previously held in 2016 and 2021.
Watching the parade with his increasingly prominent daughter - believed to be about 13 years old and named Kim Ju-ae - Kim Jong-un in a speech said his forces were capable of "immediately and thoroughly retaliating" against any hostile threat.
But the state outlet did not immediately say whether he showcased his largest weapons, including ICBMs potentially capable of reaching the US mainland.
Kim's comments has been issuing increasingly hardline views towards South Korea since 2024, when he discarded the North's goal of a peaceful reunification between the war-divided Koreas and declared the South a permanent enemy.
In a report wrapping up the congress, Kim said his government was maintaining the "toughest stance" against Washington, but added there was "no reason we cannot get along" with the Americans if they withdrew their supposedly "hostile policy" towards the North.
North Korea has repeatedly rejected Washington and Seoul's calls to resume diplomacy aimed at winding down its nuclear program, which derailed in 2019 following the collapse of Kim's second summit with US President Donald Trump during his first term.
The prospects of US-North Korea relations "depends entirely on the US attitude", Kim said.
"Whether it's peaceful coexistence or permanent confrontation, we are ready for either, and the choice is not ours to make."
