New Zealand was given a heads up by the United States before it launched an attack on a Syrian airfield.

Defence Minister Gerry Brownlee was told a few hours in advance of the attack.

Prime Minister Bill English says we were simply informed but not asked for our view.

English says he understands and United States taking action to prevent the chemical attack in Syria a few days ago occurring again.

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He says the action's supported so long as it's proportionate.

Speaking to Larry Williams on Newstalk ZB, English said he had been told that Defence Minister Gerry Brownlee "was advised an hour or two before this attack".

"But we certainly weren't asked for our opinion on it.

"We've seen horrific attacks using chemical weapons which is against all international law.

"We of course would rather see the Syrian differences resolved by diplomatic processes but the Secuirty Council hasn't been able to condemn it or do anything about it so we can understand the US taking action to prevent that kind of chemical attack occuring again - and we support action as long as it's proportionate."

New Zealand currently has 140 military trainers based in a non-combat capacity in Iraq as part of the fight against the Islamic State. It does not have a military presence in Syria.

Speaking after the airstrikes, US President Donald Trump called on "all civilised nations to join us in seeking to end the slaughter and bloodshed in Syria".

Asked in a Radio New Zealand interview what New Zealand's response to a request from the US would be, English said none had been received yet.

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"Of course if there was some request we would consider it, but that doesn't prejudge any decision."

Earlier, English appeared to be caught on the hop when asked about the US airstrikes.

He was visiting the Whangarei Town Basin and was unable to immediately comment when asked about the attack by reporters.

The Northern Advocate reported that English looked surprised and said he did not know anything about it.

His spokeswoman said the Prime Minister's office would be issuing a statement later in the day.

Foreign Affairs Minister Murray McCully said this afternoon it was becoming clear that Syrian Government forces were responsible for "outrageous" attacks in which chemical weapons were used.

"These events are horrific," he said in a statement. "It is critical that the international community emphatically demand an end to this violence, and that the Syrian government be held to account."

"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."

Security Council attempts to find a peaceful resolution in Syria have been vetoed by Russia.

While serving on the Security Council in December, New Zealand drafted a resolution to end airstrikes inSyria but it was voted down by Russia and China.

On Wednesday, McCully condemned the chemical weapons attack in northwest Syria which prompted the US military response today.

The minister said he was "appalled" to learn of a new attack in an area where chemical weapons had previously been used.

The attack was "especially horrific" because of the number of children killed, he said.

"The Security Council must take action, or we will continue to see more horrific acts like this."

Labour leader Andrew Little said unilateral action had to comply with UN resolutions.

"We do not want a repeat of what happened in Iraq. New Zealand must continue to support international efforts to find a lasting peace. Until that happens the humanitarian crisis will only get worse."

Little said he was horrified at the chemical attack, "just the latest horror in this tragic civil war".

"The world did need to express its outrage over this appalling act by the Syrian government.

"We cannot let the use of chemical weapons in violation of international law happen without consequence.

"In the end that consequence must be the international community making genuine efforts to find a solution to end the suffering of Syrians."