The New Zealand government was told in advance of US plans to bomb a Syrian air base in response to a deadly chemical attack in the civil war torn country.
Defence Minister Gerry Brownlee was told on Friday morning because of the defence partnership between the two countries.
New Zealand was not involved in the attack, his office has confirmed.
Foreign Minister Murray McCully says the government understands why the US launched dozens of cruise missile strikes against the facility controlled by Syrian leader Bashar al-Assad's forces.
"It is becoming increasingly clear that Syrian government forces were responsible for the outrageous attacks where chemical weapons were used," Mr McCully said in a statement to NZ Newswire.
"In the absence of an adequate response from the United Nations Security Council, we can understand why the United States has taken targeted unilateral action to try and prevent further such attacks by the Syrian regime."
During the strike 59 tomahawk missiles were launched at the Shayrat Airfield, near Homs, targeting aircraft, shelters, fuel, ammunition and defence systems, according to the Pentagon.
US authorities say no people were targeted and casualties are unknown.
It's the toughest direct US action yet in Syria's six-year-old civil war and raises the risk of confrontation with Russia and Iran - Assad's two main military backers.
In a press conference shortly afterward US President Donald Trump said the attack targeted the air base where the chemical weapons strike earlier this week was carried out from.
"It is in the vital national security interests of the United States to prevent and deter the spread and use of deadly chemical weapons," he said, describing the attack as "barbaric".
The Green Party have condemned the attack while a UN Security Council investigation is underway.
"This is not the moment for a military action by the US against a country where a Russian military presence already exists," global affairs spokesman Kennedy Graham said.
"The US President should recognise that precautionary multilateral measures, not precipitate unilateral actions, are the appropriate way to proceed in today's dangerous world."