A UN inspection team, headed by Hans Blix, was in Iraq investigating the situation but had yet to complete its investigation. Having sought but failed to get authorisation from the UN Security Council, the Bush administration decided there was no point waiting any longer. The time had come to strike. To gain international support for its decision the US produced evidence suggesting Saddam Hussein's regime was developing – and possibly intending to use – weapons of mass destruction. Most experts and governments – and world public opinion – remained unconvinced. And so it was that the US set out on a military adventure, based at best on shaky legal grounds. Getting rid of Saddam proved the easy part. No WMD were found. But what was meant to be a limited intervention turned out to be a protracted one that left the US demoralised and Iraq in ruins.

Prolonged sectarian violence, which continues to this day, has generated a destabilising dynamic that now engulfs much of the Middle East. Ten years later the Obama administration, with the support of a few European governments, is on the verge of embarking on a similarly ill-conceived expedition. Last time it was Britain that bolstered an otherwise feeble coalition. This time the hope is that France will come to the party. Several Arab countries, including Egypt and Jordan, have already indicated they oppose military intervention. US Secretary of State John Kerry claims to have conclusive evidence that the Assad government has launched a chemical attack on its people, and argues that such actions must not go unpunished. Obama has spoken of a limited strike not aimed at regime change. But what is the reality? The indications are that a chemical weapons attack did take place in the Damascus suburb of Ghouta. But we know little about the chemicals used – though sarin gas has been mentioned frequently – the means of delivery or their provenance.

The US intelligence report released on Friday speaks of more than 1400 casualties – but this and other details given are asserted rather than demonstrated. As for the sources of the evidence we are simply referred to general categories, much of it available on the public record, and generally regarded as less than conclusive. As for motive, US policymakers remain remarkably silent. Why should Assad decide to use chemical weapons at a time when his forces are making considerable gains against the rebels? And why should he do it at the moment that UN inspectors are inside the country and within 10 minutes' reach of the site of destruction? And the possibility of one or other of the rebel groups acquiring such weapons has been all too easily dismissed. It is only three months since Carla del Ponte, a member of the UN Independent Commission of Inquiry on Syria, announced she had "strong concrete suspicions" that rebels had used the nerve gas sarin. The sarin attack on the Tokyo subway in 1995, which killed 13 people, severely injured 50 and caused temporary vision problems for nearly a thousand others, was the work of a small unaided cult group. One of the well organised and internationally supported rebel groups would, one assumes, be capable of inflicting much greater havoc.

With evidence that is still less than conclusive, Obama appears on the verge of repeating the mistakes of his predecessor – assuming he is able to persuade Congress to vote for the proposed strike. If he does go ahead, he will, like Bush, be doing so on dubious legal grounds. Even if it is established that the Syrian army did carry out the chemical attack, the US is not under direct military threat – it is not therefore acting in self-defence. And, in the absence of UN Security Council authorisation, which will not be forthcoming, the "responsibility to protect" principle does not allow third parties to take matters into their own hands. In any case, why not wait, at least for the UN inspection team to complete its report? Why discredit the credibility of its investigation before it has had a chance to submit its report. The Syrian government claims it has given the UN inspectors clear evidence that it was not responsible for the attack. Why not wait to see what the inspectors make of such claims? If it goes ahead, a US military strike on Syria will be the ninth Western military intervention in a Muslim country in 15 years. The gains thus far for peace and security have been negligible and the costs for the authors and victims of intervention nothing short of horrendous.

A US military foray into Syria will reopen Pandora's box. What will the US do if, as seems likely, the planned "limited strike" fails to achieve its objective of intimidating Assad? In all probability, the US and its allies will be tempted to take additional military action, with incalculable consequences for Syria, and for regional and global security. As UN Secretary-General Ban Ki-moon and Pope Francis have stated in clear language, only a politically negotiated solution offers any prospect of peace in Syria and the reconstruction of that war-torn country. An Australian government wishing to exercise the limited leverage afforded by membership of the Security Council would do well to press for this option in the difficult days and weeks ahead Joseph Camilleri is Emeritus Professor, La Trobe University and founding director of the Centre for Dialogue.