Chemical, biological and nuclear weapons poison and kill indiscriminately, as distinct from weapons that can be precisely used against military targets. That is why weapons of mass destruction have been proscribed and powerful civilised nations must ensure any use of them is effectively punished. The only question arising from the punitive strike at Syria's regime at the weekend is, will it be effective?

Chemical weapons have been used three times against rebel enclaves during Syria's long civil war. After the first instance, on April 29, 2013, US President Barack Obama was persuaded to step back from his "red line" declaration and make a joint effort with Russia to place Syria's chemical arsenal under international control.

So much for trusting Russia. In April last year the same chemical, the nerve agent sarin, was used in an attack on the Syrian town Khan Sheikhoun, killing more than 80 people, many of them children. After that second offence, the US carried out a punitive strike on a Syrian airfield. But a year later the regime resorted to chemical weapons again, gassing hundreds of people in Douma near Damascus this month.

The US response this time, supported by France and Britain, has done considerably more damage than a year ago. Their missiles have destroyed military buildings said to be used in Syria's chemical weapons programme. There have been no reports of human casualties, nor retaliatory moves by Russia to launch its anti-missile missiles. Clearly the targets were obvious, or made known, to the regime in the week that President Donald Trump was tweeting his intentions to the world.

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This was another carefully calibrated military action designed to send a message without risking an escalation of the war. But was it enough? Is the "message" about chemical weapons any clearer or more convincing than it was a year ago? Perhaps not. But with the Syrian regime winning the war thanks to Russia's support, and the US largely disengaged, nothing was to be gained by a more deadly strike.

Russia and its client regime may be able to ignore the latest "message" just as they did the previous responses, but it is nevertheless vital that the world does respond in this way. Ideally, the United Nations would have the cohesion and strength to deal a punitive blow to any country that uses a chemical weapon against another or against its own people. But in the real world, the use of these weapons has to be punished by those who possess the necessary principles and power.

The US could perform this role alone if it had to. This time it has had the active military support of Britain and France and the moral support of other Western allies. Sadly, it is not clear whether New Zealand is among them. Prime Minister Jacinda Ardern has expressed regret that the UN is hamstrung and "accepts" the US, France and Britain have taken action. "Accepts" is not exactly support.

Her Government should unequivocally support the message that chemical weapons can not be used with impunity. To let these weapons go unpunished would be dangerous for us all.