New Zealand will present its legal view on Russia's invasion of Ukraine at the United Nations' international court, contesting the Kremlin's claim of genocide.
It marks New Zealand's second legal intervention - where a country not party to a case presents its views - at the International Court of Justice, having previously backed Australia's case against Japanese whaling in 2012.
In a statement, Minister of Foreign Affairs Nanaia Mahuta and Attorney-General David Parker said New Zealand would challenge Russia's "spurious attempt to justify its invasion under international law".
Ukraine's case, filed in February, argues Russia falsely claimed genocide had occurred in the Luhansk and Donestk regions as justification for its so-called "special military operation" - the invasion of Ukraine.
It seeks a ruling that no acts of genocide occurred in those regions, and that Russia had no lawful basis to invade.
New Zealand's intervention could include written, and possibly oral, submissions and puts its legal view on the record. It recently joined 40 other countries in backing a Canada-led statement indicating they would consider making a third-party intervention.
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Parker said New Zealand had a real interest in ensuring the Genocide Convention was properly interpreted and applied.
"Disputes between states should be resolved by peaceful means, including through the ICJ, and not by the illegal use of force," he said.
Mahuta said the invasion, and Russia's "disingenuous attempt to justify it under the Genocide Convention" was a significant threat to basic principles of international law, the UN charter, and the rules-based international system.
"Aotearoa New Zealand is prepared to play its part in assisting Ukraine and has already done so through a range of diplomatic, military and economic measures," she said.
"We are profoundly concerned about the loss of life and human suffering in Ukraine as a result of Putin's illegal invasion."
Ukraine's substantial case is due to be filed with the ICJ by 23 September.