North Korea passed a law enshrining the right to use preemptive nuclear strikes to protect itself, a move leader Kim Jong Un said makes its nuclear status "irreversible" and bars any denuclearisation talks, state media reported on Friday.

The move comes as observers say North Korea appears to be preparing to resume nuclear testing for the first time since 2017, after historic summits with then-U.S. President Donald Trump and other world leaders in 2018 failed to persuade Kim to abandon his weapons development.

The North's rubber-stamp parliament, the Supreme People's Assembly, passed the legislation on Thursday as a replacement to a 2013 law that first outlined the country's nuclear status, according to state news agency KCNA.

"The utmost significance of legislating nuclear weapons policy is to draw an irretrievable line so that there can be no bargaining over our nuclear weapons," Kim said in a speech to the assembly, adding that he would never surrender the weapons even if the country faced 100 years of sanctions.

A deputy at the assembly said the law would serve as a powerful legal guarantee for consolidating North Korea's position as a nuclear weapons state and ensuring the "transparent, consistent and standard character" of its nuclear policy, KCNA reported.

"Actually spelling out the conditions for use are especially rare, and it may simply be a product of North Korea's position, how much it values nuclear weapons, and how essential it sees them for its survival," said Rob York, director for regional affairs at the Hawaii-based Pacific Forum.

PREEMPTIVE STRIKES

The original 2013 law stipulated that North Korea could use nuclear weapons to repel invasion or attack from a hostile nuclear state and make retaliatory strikes.

The new law goes beyond that to allow for preemptive nuclear strikes if an imminent attack by weapons of mass destruction or against the country's "strategic targets", including its leadership, is detected.

"In a nutshell, there are some really vague and ambiguous circumstances in which North Korea is now saying it might use its nuclear weapons," Chad O'Carroll, founder of the North Korea-tracking website NK News, said on Twitter.

"I imagine the purpose is to give U.S. and South Korean military planners pause for thought over a much wider range of actions than before," he added.

Like the earlier law, the new version vows not to threaten non-nuclear states with nuclear weapons unless they join with a nuclear-armed country to attack the North.

The new law adds, however, that it can launch a preemptive nuclear strike if it detects an imminent attack of any kind aimed at North Korea's leadership and the command organization of its nuclear forces.

That is an apparent reference to South Korea's "Kill Chain" strategy, which calls for preemptively striking North Korea's nuclear infrastructure and command system if an imminent attack is suspected.

Kim cited Kill Chain, which is part of a three-pronged military strategy being boosted under new South Korean President Yoon Suk-yeol, as a sign that the situation is deteriorating and that Pyongyang must prepare for long-term tensions.

'RESPONSIBLE NUCLEAR STATE'

The law also bans any sharing of nuclear arms or technology with other countries, and is aimed at reducing the danger of a nuclear war by preventing miscalculations among nuclear weapons states and misuse of nuclear weapons, KCNA reported.

Analysts say Kim's goal is to win international acceptance of North Korea's status as a "responsible nuclear state."

U.S. President Joe Biden's administration has offered to talk to Kim any time, at any place, and Yoon has said his country would provide massive amounts of economic aid if Pyongyang began to give up its arsenal.

South Korea on Thursday offered to hold talks with North Korea on reunions of families separated by the 1950-53 Korean War, in its first direct overture under Yoon, despite strained cross-border ties.

North Korea has rebuffed those overtures, however, saying that the United States and its allies maintain "hostile policies" such as sanctions and military drills that undermine their messages of peace.

"As long as nuclear weapons remain on earth and imperialism remains and manoeuvres of the United States and its followers against our republic are not terminated, our work to strengthen nuclear force will not cease," Kim said.