Australia led secret diplomatic efforts to frustrate a New Zealand-led push for nuclear disarmament, according to documents released under freedom of information laws.
The move has been attacked by Opposition politicians here but New Zealand Prime Minister John Key and Foreign Affairs Minister Murray McCully downplayed the split with Australia.
Declassified ministerial submissions, cables and emails from Australia's Department of Foreign Affairs and Trade show Australian diplomats worked energetically against nuclear disarmament efforts by other countries, because "we rely on US nuclear forces to deter nuclear attack on Australia".
In October last year, following the election of the Coalition government, Australia refused a New Zealand request to endorse a 125-nation joint statement at the United Nations highlighting the humanitarian consequences of any use of nuclear weapons.
It objected to a sentence declaring that it was in the interest of humanity that nuclear weapons were never used again, "under any circumstances".
Key said Australia was in "a slightly different perspective ... and used "different language" on the issue.
It was not arguing that nuclear war was in anyone's interest anywhere.
New Zealand had a long and proud history of being nuclear free. It was inevitable it would have a different position from Australia, which was a part of the Anzus alliance with the United States and produced uranium, Key said.
It would not be in New Zealand's best interest for the US to ever deploy nuclear weapons to protect this country.
"The times in history when nuclear weapons have been deployed ... there have been horrific outcomes as a result of that. Whatever the motivations or reasons, (it would) not be in the world's best interests."
McCully said the Government respected Australia's right to take a different stance.
"We were pleased with the overwhelming support for our resolution Humanitarian Consequences of Nuclear Weapons and respect Australia's right to an alternative view."
But Greens foreign affairs spokesman Kennedy Graham said it was "more of the same" from Australia and was in line with the stance it had taken in the 1980s.
"It's sad but not a surprise ... They are saying they are safer with nuclear deterrence, we are saying we are safer without it."
He said the logic, if you reversed it, was that the Abbott government believed there were circumstances when it would be in the global interest to use nuclear weapons.
"If you turn the logic that way it's a pretty extraordinary statement."
Labour spokeswoman Maryan Street said Australia's actions struck a jarring note in trans-Tasman relations.
"Australia has every right to take a different position from us on these matters. However, the argument that possession of, or access to, nuclear warheads is a modern deterrent, is so outdated now it would be laughable if it were not so serious," she said.
"How can it profit the world for nuclear weapons to exist as the ultimate threat? We seek to rid Syria of chemical weapons, minimise Iran's nuclear capability, and yet somehow think it is okay to retreat behind a nuclear shield which could destroy us all."
A group of 16 nations, including Indonesia, Malaysia, Mexico, South Africa and New Zealand, have been working to highlight the humanitarian impacts of nuclear weapons.
This diplomatic campaign was intended to lay the ground for negotiation of a convention that would prohibit nuclear weapons - putting them in the same category as chemical and biological weapons which were already prohibited under international law.
Australia's foreign affairs minister, Julie Bishop, has argued this approach was simply counterproductive.
"[The] argument 'to ban the bomb' may be emotionally appealing, but the reality is that disarmament cannot be imposed this way," she said last month.
"Just pushing for a ban would divert attention from the sustained, practical steps needed for effective disarmament."
However, declassified documents have revealed the government's primary concern was that a nuclear weapons ban would "cut across" Australia's reliance on US nuclear deterrence as part of its defence posture.
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