Prime Minister Jacinda Ardern says Donald Trump's decision to withdraw from the Iran deal is "disappointing".
US President Donald Trump today announced the US will withdraw from the nuclear deal with Iran and reimpose sanctions.
Mr Trump has been highly critical of the 2015 accord, under which Iran limited its nuclear activities.
The president's announcement took place around 6.15am NZT. In the announcement he called the deal "defective at its core."
"This was a horrible one-sided deal that should have never, ever been made," Mr Trump said at the White House. "It didn't bring calm. It didn't bring peace. And it never will."
The president said the US will institute the "highest level" of sanctions against Iran.
Ms Ardern said the decision was "disappointing."
"Our view is that it made for a more stable, predictable Middle East," she said.
EU powers see the deal as the best way to stop Iran developing a nuclear bomb and their officials met a senior Iranian on Tuesday without US officials present.
In a statement, France, Germany and the UK - who are also signatories to the deal - have said they "regret" the American decision.
The European Union's top diplomat, Federica Mogherini, said the EU was "determined to preserve" the deal.
National Party leader Simon Bridges said he sided with Europe on the withdrawal.
"My inclination is to be more on the side of Merkel, May and Macron than President Trump on this," he said.
"It was a complex, difficult deal that does seem to be making a difference in relation to nuclear capability and weaponry in Iran," Mr Bridges said.
But Israel's Prime Minister Benjamin Netanyahu said he "fully supports" Mr Trump's "bold" withdrawal from a "disastrous" deal.
Saudi Arabia also welcomed Mr Trump's decision.
"Iran used economic gains from the lifting of sanctions to continue its activities to destablise the region, particularly by developing ballistic missiles and supporting terrorist groups in the region," according to a statement carried on Saudi-owned Al Arabiya television.
Sunni Muslim Saudi Arabia, a key US ally, has been at loggerheads with Shi'ite Iran for decades, and the countries have fought a long-running proxy war in the Middle East.
After Mr Trump's announcement, Iranian state television said that decision to withdraw from the deal was "illegal, illegitimate and undermines international agreements".
Earlier, Iran's President, Hassan Rouhani, said his country will continue to seek "constructive relations" with the world.
Envoys of Germany, France and the UK discussed the situation with Iran's Deputy Foreign Minister Abbas Araghchi in Brussels on Tuesday, an EU statement said.
An unnamed German official told Reuters news agency that representatives of the countries had been in contact for weeks.
"In the coming days, it will also be important to remain in discussion with all sides to avoid an uncontrolled escalation," the official said.
What was agreed under the deal?
The so-called Joint Comprehensive Plan of Action (JCPOA) saw Iran agree to limit the size of its stockpile of enriched uranium - which is used to make reactor fuel, but also nuclear weapons - for 15 years and the number of centrifuges installed to enrich uranium for 10 years.
Iran also agreed to modify a heavy water facility so it could not produce plutonium suitable for a bomb.
In return, sanctions imposed by the UN, US and EU that had crippled Iran's economy were lifted.
The deal was agreed between Iran and the five permanent members of the UN Security Council - the US, UK, France, China and Russia - plus Germany.
Iran insists its nuclear programme is entirely peaceful, and its compliance with the deal has been verified by the International Atomic Energy Agency (IAEA).
Why does Mr Trump oppose it?
Mr Trump has called the deal a "disaster" and "insane" and twice refused to certify to Congress that Iran is complying with it.
In January, he warned that the US would "withdraw" from the accord on 12 May - the next deadline for waiving sanctions - unless its "disastrous flaws" were fixed.
He complained that the deal only limited Iran's nuclear activities for a fixed period; had failed to stop the development of ballistic missiles; and had handed Iran a $US100bn windfall that it used "as a slush fund for weapons, terror, and oppression" across the Middle East.
European leaders attempted to persuade Mr Trump that his concerns could be addressed through a supplemental agreement.
But European diplomats reportedly concluded on Monday that they had failed.
What could Mr Trump announce?
The president could immediately hit Tehran with a barrage of oil and banking sanctions, along with measures targeting Iranian companies - a hard exit that the BBC's Nick Bryant in Washington said could effectively kill the entire deal.
However, the White House has signalled that he will stop short of that.
Officials told the Associated Press that Mr Trump might reimpose sanctions on Iran's central bank, which would hit Iran's oil exports, and give foreign companies doing business with Iran a six-month grace period to wind down operations before incurring penalties.
He also does not need to issue waivers for other sanctions until later this year, including those targeting 400 Iranian companies, individuals and business sectors.
What has Iran said?
President Rouhani told an audience of oil and gas executives in Tehran on Tuesday morning that if Mr Trump chose to reimpose sanctions, Iran would "face some problems for two or three months" but would "pass through this".
He stressed that "the foundation of our policy is to work and have constructive relations with the world" - an apparent reference to other parties to the deal.
But others within his government struck a different tone.
It "will not be in the Americans' interest" if they cause the deal to collapse, the secretary of Iran's Supreme National Security Council said.
Iran "will not be passive if the US starts confrontation" with it, Fars news agency also quoted Ali Shamkhani as saying.
The speaker of the Iranian parliament, Ali Larijani, said the US "did not implement their commitments", seemingly anticipating a withdrawal.
"It seems you can only speak with the Americans in the language of force, and there is no other solution."
Mr Rouhani represents the more moderate face of Iran's leadership, and he helped finalise the nuclear deal in a bid to ease the desperate state of Iran's economy.
Correspondents say there are other more hardline forces in Iran that never embraced the agreement and would not be unhappy to see it undermined.
- BBC and Reuters