Last month Pyongyang put a spy satellite into space – and claims it has since photographed major US and South Korean military sites.
Setting out his aims for 2024, Kim Jong Un also said his dealings with South Korea would see “fundamental change”.
And he said he had no option but to press ahead with his nuclear ambitions.
Speaking at an end-of-year meeting of the ruling Workers’ Party of Korea, Mr Kim said unification with South Korea was now no longer possible. He said Seoul treats his country as an enemy.
It appears to be the first time Mr Kim has said such a thing and marks an official change in policy – although in practice there has been little prospect of unification for some years, with no progress and little effort being made.
Relations between the two countries are in a poor state. Last month, following the spy satellite launch, Pyongyang ripped up a deal with Seoul that was aimed at lowering military tensions.
North Korea also continued regular tests of its missiles throughout 2023 – and earlier this month fired its most advanced long-range missile, defying UN curbs.
The launch of the intercontinental ballistic missile – which has the range to reach the North American continent – drew immediate condemnation from the West.
Meanwhile North Korea is unhappy over South Korea ramping up defence cooperation with the US, after a US submarine armed with nuclear weapons arrived in its waters.
Following Mr Kim’s comments on Sunday, South Korea’s defence ministry condemned any plans to use nuclear weapons against Seoul.
In a statement, the defence ministry said South Korea would retaliate “overwhelmingly”, with the support of the US, “and the Kim Jong-Un regime will face its end”. BBC News