New Zealand can't commit to an aggressive response against North Korea while encouraging other parties to avoid escalating the situation, Foreign Minister Gerry Brownlee says.
Australian Prime Minister Malcolm Turnbull on Friday committed to supporting the US in the event of an attack by North Korea, but New Zealand won't make the same promises.
Mr Brownlee says instead that now is a time for caution.
"Committing to an aggressive response now - while encouraging all involved to avoid escalation - is not a position we want to take," he said from Fiji where he is meeting his Pacific region counterparts.
Mr Brownlee said Australia was New Zealand's only formal ally and if an armed conflict did develop options would be assessed at the time.
Earlier Prime Minister Bill English said any military support for the US would be considered "on its merits".
He said any military support at this stage is hypothetical and he's still focused on a "peaceful resolution" of nuclear threats between the two nations.
"While there's been an escalation of rhetoric there isn't any indication that military action's going to occur," he said.
"We're in close contact with the US and Australia but any decision New Zealand makes about North Korea we make according to our own interests."
Under the ANZUS Treaty, in effect since 1952, Australia is obliged to back the US in the event of an attack like that threatened by North Korean leader Kim Jong Un on Guam, through the ANZUS treaty.
US-New Zealand obligations under the treaty have been suspended since 1984.
Mr Turnbull said Australia would invoke the treaty.
"In terms of defence, we are joined at the hip," he told Australia's 3AW radio on Friday.
US President Donald Trump this week threatened North Korea with "fire and fury", which was derided as a "load of nonsense" by North Korea's military.
He upped the ante later in the week, telling reporters the fire and fury comment maybe "wasn't tough enough".
Mr English said he didn't want to see comments that escalate the tension, again describing Mr Trump's latest remarks as "not helpful".
"The US does remain committed to working to resolve these issues without military intervention," he said.
He remains focused on peaceful resolution, working with the UN, US, China and Russia to put pressure on North Korea.