The message came in a statement carried by state media and attributed to the powerful National Defence Commission.
“We declare solemnly and confidently that the foolish politicians around the world, including the puppet group in South Korea, should not expect any change from us,” it said.
North Korea’s neighbours are watching to see whether the leadership change will affect Pyongyang’s ties with the international community.
The impoverished communist state remains technically at war with South Korea and is isolated on the international stage because of its dire human rights record and pursuit of nuclear weapons.
Six-nation talks aimed at ending Pyongyang’s nuclear ambitions – involving the two Koreas, China, the US, Russia and Japan – have been stalled for months.
The statement from the NDC – which is thought to be the country’s top decision-making body – said North Korea would “never deal” with South Korean leader Lee Myung-bak.
Mr Lee has angered Pyongyang by linking the provision of aid to progress on denuclearisation.