North Korea has accused the US of planning to dominate the whole of Asia and occupy the Korean peninsula.
Vice-foreign minister Pak Kil-yon told the UN General Assembly in a long-awaited speech: "Due to the continued US hostile policy towards DPRK [Democratic People's Republic of Korea], the vicious cycle of confrontation and aggravation of tensions is an ongoing phenomenon on the Korean peninsula, which has become the world's most dangerous hotspot where a spark of fire could set off a thermonuclear war.
"At the root of the US policy, which has continued for over half a century, lies the intention to destroy the ideas and the system chosen by our people and to occupy all the Korean peninsula and use it as a stepping stone for realising its strategy of dominating the whole of Asia."
Pak accused the UN of adopting an "unjust" statement under US pressure with its condemnation of a ballistic missile launch made by the North - despite the failure of the rocket, which broke up less than two minutes into its flight.
As a gesture of its disapproval, the US cut food aid to North Korea.
According to the DPRK the launch was aimed to put a satellite into orbit.
Pak also criticised the South Korean government of Lee Myung-bak and its hardline strategy towards the North.
"The current South Korean government has caused the worst situation in North-South relations by making all inter-Korean agreements null and void," Pak said.
"History will bring them to justice."
Geopolitical analysts believe that North Korea's growing stridency is aimed at influencing elections in the South in December.