"The DPRK's nuclear force-building policy has been made permanent as the basic law of the state, which no one is allowed to flout with anything," leader Kim Jong Un said at a meeting of the State People's Assembly that was held Tuesday and Wednesday, the KCNA news agency said.

DPRK is the acronym for the country's formal name.

North Korea has conducted a record number of weapons tests this year and relations with South Korea and the United States are very tense, amid fears that Pyongyang might conducts its first nuclear test since 2017. It has conducted six in all since 2006.

A year ago the assembly passed a law declaring North Korea to be a nuclear weapons state and Kim said this status was "irreversible." That new law also allowed for the pre-emptive use of nuclear weapons.

Now, the assembly has gone further by stipulating that nuclear weapons status in the constitution itself.

"This is a historic event that provided a powerful political lever for remarkably strengthening the national defense capabilities," Kim said, according to KCNA.