Prime Minister Jacinda Ardern has warned the United Nations the rules of nuclear warfare had changed and that "leaders amongst us" believed that they could start and win a nuclear war, even if it meant sacrificing the lives of their own citizens - a thinly-veiled reference to Russia.
Ardern said New Zealand had "never accepted the wisdom of mutually assured destruction" and warned that some leaders now believed that they could start and win a nuclear war.
"It takes one country to believe that their cause is nobler, their might stronger, their people more willing to be sacrificed," she said.
"None of us can stand on this platform and turn a blind eye to the fact that there are already leaders amongst us who believe this."
This represents a stark reversal to the rules that underpinned the nuclear doctrines of the end of the Cold War, best summed-up by a often-repeated joint statement from US and Soviet leaders Ronald Reagan and Mikhail Gorbachev: "A nuclear war cannot be won and must never be fought."
Ardern's line was a reference to an address made by Russian President Vladimir Putin this week as he called up 300,000 reservists for his invasion of Ukraine and threatened to use nuclear weapons to defend Russia's territorial integrity - a territory that could soon include more unlawfully annexed parts of Ukraine.
She made the comments in a speech to the United Nations General Assembly, the centrepiece of her trip to New York this week.
Ardern earlier said she had rewritten "a little bit" of her speech after Putin's escalation of the conflict on Wednesday this week.
"Nuclear weapons do not make us safer," she said in the speech.
"There will be those who agree but believe it is simply too hard to rid ourselves of nuclear weapons at this juncture.
"There is no question that nuclear disarmament is an enormous challenge. But if given the choice, and we are being given the choice, surely we would choose the challenge of disarmament than the consequences of a failed strategy of weapons-based deterrence."
Ardern made a pitch for countries to get back around the negotiating table for the Nuclear Non-Proliferation Treaty, the UN treaty that is the centrepiece of efforts to halt the spread of nuclear weapons.
A key summit on that treaty failed to reach agreement this year, thanks to Russia vetoing progress - an act Disarmament Minister Phil Twyford called "diplomatic sabotage".
Ardern called out Russia by name, saying "progress and consensus" on the treaty "was recently blocked by Russia".
She said this represented a "backwards step to the efforts of nearly every country in the world to make some even limited progress on nuclear disarmament and non-proliferation".
The 20-minute speech also touched on climate change and the threats of online misinformation.
Ardern said a period of "loss", like the loss of the pandemic, brings "a chance for reflection".
"Between us we represent countries and communities who have lost much in these past few years," she said.
Ardern warned Covid continued to hit economies and people and that it "set us back in our fight against the crisis of climate change".
"We move between one another's countries with increasing ease. We trade our goods and services. And when one link in our supply chain is impacted, we all are," she said.
Ardern said the lessons of the pandemic were "in many ways the same as the lessons of climate change": that the world is interconnected and global efforts to combat threats are only as successful as the least-committed country allows them to be.
"When crisis is upon us, we cannot and will not solve these issues on our own," she said.
"The next pandemic will not be prevented by one country's efforts, but by all of ours. Climate action will only ever be as successful as the least committed country, as they pull down the ambition of the collective.
"I am not suggesting though that we rely on the goodwill of others to make progress. We need a dual strategy. One where we push for collective effort, but we also use our multilateral tools to make progress."
Ardern said she backed an international effort to "develop a new global health legal instrument, strengthened international health regulations and a strong and empowered World Health Organisation".
She said countries needed to keep supply chains open and to ensure that "critical goods and services are not subjected to protectionism in times of need".
A theme of the high-level week at the United Nations General Assembly has been reform of broken institutions like the Security Council.
US President Joe Biden used his speech to the General Assembly to say that the United States was open to limited reform of the council, by expanding its membership beyond 15, and expanding the number of permanent, veto-wielding members.
Biden said states should "refrain from the use of the veto, except in rare, extraordinary situations, to ensure that the Council remains credible and effective".
But he stopped short of saying the veto should be axed altogether.
Ardern said New Zealand championed a new initiative which allows the General Assembly, which includes all UN member states, to scrutinise any use of the veto by one of the permanent five members of the Security Council.
But she said that for the "United Nations to maintain its relevancy, and ensure that it truly is the voice of the breadth of countries it represents", reform of the veto had to go further - to the point where it was abolished completely.
"The veto must be abolished and Permanent Members must exercise their responsibility for the benefit of international peace and security, rather than the pursuit of national interest," Ardern said.