"Recently, at a meeting of the International Atomic Energy Agency's Board of Governors, the US once again committed a grave political provocation by branding our possession of nuclear weapons as illegal and clamouring about denuclearisation," the North's UN mission said in a statement carried by the official Korean Central News Agency.

The status of North Korea "as a nuclear-armed state, enshrined permanently in the nation's supreme and fundamental law, has become irreversible", the statement said, noting the country has not had "official relations" with the nuclear watchdog for more than 30 years.

The IAEA has "neither the legal authority nor the moral justification to interfere in the internal affairs of a nuclear-armed state that exists outside the Nuclear Non-Proliferation Treaty", it said.

North Korea withdrew from the IAEA in 1994 after a standoff over nuclear inspections, claiming the agency was being used by Washington to infringe on its sovereignty.

Pyongyang will "firmly oppose and reject any attempt to alter the current status of the Democratic People's Republic of Korea, and, as a responsible nuclear-armed state", the statement added, using the official name of North Korea.

The statement follows North Korean leader Kim Jong Un's visit to weapons research facilities last week, where he said Pyongyang "would put forward the policy of simultaneously pushing forward the building of nuclear forces and conventional armed forces."

Since a failed summit with the United States in 2019 on denuclearisation, North Korea has repeatedly said it will never give up its nuclear weapons.