We may never know how many were killed in the initial storm and tidal surge of Cyclone Nargis. The estimate of 100,000 deaths is widely accepted, and well over a million more are probably now at serious risk from epidemic and other threats.

What we do know is that the crucial initial failure was one of prevention - many of the tens of thousands who died could have been saved.

The Burmese authorities had two days' warning from the Indian government about the path of the cyclone and what the likely impact would be on the Irrawaddy Delta and beyond. They failed to make any attempt to evacuate people or make preparation for a massive relief effort.

Experience from Bangladesh and India, where deaths from cyclones and storm surges have been reduced dramatically, shows what can be done with relatively modest investment in early warning systems and related infrastructure and evacuation procedures. Taking such measures is part of what it means to be politically responsible in countries exposed to such natural hazards.

Whatever the exact numbers and the intransigence of the government, there is no doubting the scale of the relief and recovery needs, which are likely to be compounded by a further escalation in food prices.

Those international nongovernmental organisations unable to operate freely themselves are looking for ways to provide some immediate assistance through local partners. The U.N. agencies are limited to working through official channels and trying to negotiate an easing of entry and operating restrictions.

Much of what assistance is available, is coming through the efforts of the monasteries, local organisations and ordinary people.

The United Nations in its humanitarian functions can only act on invitation, and the current crisis presents an extreme case of a much more general problem: it is the crisis-affected state itself that gets to "call" a crisis and to invite international assistance, on terms that it sets itself.

Such crises can be politically embarrassing, not least because they are almost always defined by an overwhelming of state capacity. Admitting the existence of a crisis may be tantamount to saying "we can't cope", and affected states have a history of being reluctant to acknowledge the extent of their own incapacity to respond.

For a regime as sensitive to criticism - internal and external - as the current Burmese government, this is a particularly potent factor.

Bernard Kouchner, the French foreign minister, called last week for the U.N. Security Council to consider the Burma crisis under the heading of the "responsibility to protect" doctrine endorsed at the 2005 World Summit, opening the way for the use of force if necessary.

China, Russia and others were quick to say that this was not a matter for the Security Council. It was a call that was always likely to harden attitudes and Kouchner may have been stretching a point: it is not clear that the responsibility to protect doctrine covers such cases, unless perhaps (as Gareth Evans, President of International Crisis Group, and others have suggested) this is construed as a "crime against humanity".

But Kouchner is the man who championed the droit d'ingerence (right of interference) in setting up the aid agency Médecins Sans Frontières. Whatever view one takes on his statement last week, the truth at the heart of it is that such a gross failure of state responsibility towards its own people ought to give rise to an international responsibility to act.

How to define the scope and limits of this idea has been much debated in the past two decades: what kinds of action are warranted, in what circumstances and under what authority?

The use of force against another country is at the extreme end of a spectrum of possible diplomatic and coercive measures usually considered only in the light of a threat to international peace and security. Consensus on the "responsibility to protect" doctrine has not been matched by agreement on how to apply it.

At the international level, questions of law and politics are often hard to distinguish, and are usually complicated by debates about what might actually work.

Even those advocating airdrops of food and other supplies - an instinctively appealing idea - acknowledge that such actions alone are unlikely to be enough. Others say they would be counter-productive and a distraction from the real needs.

Technical skills and massive logistical capacity are lacking and urgently needed, but without a formal request they could not be introduced without risking direct confrontation with the Burmese authorities.

Even if it were willing, the Burmese government lacks the helicopters and transport systems to mount operations on the necessary scale, and anyway it shows little sign of deploying the full resources of its 400,000-strong army.

Meanwhile, various forms of "loud" and "soft" diplomacy are being pursued. The United Nations is proposing the establishment of air and sea bridges, while others are looking to work under the radar in whatever way they can.

The situation in Burma is an extreme case of a more common phenomenon of state denial. How to reduce the political stigma of calling for international assistance?

Given the ambiguity surrounding current legal and political doctrine, it may be that an international convention that sets out both the responsibilities of crisis-affected states and of those providing assistance would be desirable.

Current work on international disaster law certainly deserves greater priority. But the obstacles to progress at the international level are substantial - and the more immediate answers lie in the political contract between the state and its people.

In its response to the Szechuan earthquake, China has demonstrated how far it has come in this respect. In Bangladesh and India too, protection against natural hazard is understood as part of the political "deal" and government performance is watched closely by the media.

People ultimately need to judge the performance of their own rulers, but they are not passive bystanders. The combined efforts of hundreds of thousands of volunteers, often coordinated through the Red Cross and Red Crescent, has proved a vital ingredient in effective prevention and response efforts in these countries.

While the Burmese authorities failed to act in the face of clear warnings, Burma is certainly not uniquely culpable in its failure to invest in systems of prevention and response.

Even the wealthy United States was caught unprepared with Hurricane Katrina. But here and in a growing number of other places in the world - thanks to global warming and increasing numbers living in marginal habitats - people's exposure is such that unless preventive action is taken now, countless thousands more will die needlessly in future.

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