The Supreme People's Assembly unanimously adopted the revision that states North Korea "develops highly nuclear weapons to ensure" its "rights to existence" and to "deter war", news agency KCNA reported, after the conclusion on Wednesday of a two day-meeting of the North's rubber-stamp parliament.
"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," North Korean leader Kim Jong-un said, addressing the parliament.Â
DPRK are the initials of the North's official name, the Democratic People's Republic of Korea.
Kim went on to stress "the need to push ahead with the work for exponentially boosting the production of nuclear weapons and diversifying the nuclear strike means and deploying them in different services".
And he said US military drills and deployment of strategic assets in the region were extreme provocations.
South Korea's unification ministry said the revised constitution showed Pyongyang's "strong will" not to abandon its nuclear program.
"We once again stress that North Korea will face an end of its regime if it uses nuclear weapons," it warned in a statement.
Japanese Chief Cabinet Secretary Hirokazu Matsuno said North Korea's nuclear and missile development posed threats to the "peace and safety of our country and the international community - and can never be tolerated".
The amendment comes a year after North Korea officially enshrined in law the right to use pre-emptive nuclear strikes to protect itself, a move Kim had said would make its nuclear status "irreversible".
Kim urged officials to further promote solidarity with the nations standing against the US, denouncing trilateral co-operation between the US, South Korea and Japan as the "Asian-version NATO".
"This is just the worst actual threat, not threatening rhetoric or an imaginary entity," he said.
Kim returned home last week from a trip to Russia during which he and Russian President Vladimir Putin agreed to boost military and economic co-operation.
US and South Korean officials have expressed concern that Pyongyang could be seeking technological help for its nuclear and missile programs while Moscow tries to acquire ammunition from the North to supplement its dwindling stocks for the war in Ukraine.
Analysts said having the nuclear policy written into the constitution was a symbolic move, declaring the North's intention to have a permanent nuclear force that it would not negotiate over.
"The new Cold War in the Northeast Asia region and military tensions on the Korean peninsula will intensify," said Yang Moo-jin, a professor at the University of North Korean Studies in Seoul.
On Tuesday, South Korean President Yoon Suk Yeol warned Pyongyang of an "overwhelming response" if it used nuclear weapons, as Seoul put on the first large-scale military parade in a decade in a show of force.
