Five former Nato generals, including the former chairman of the US Joint Chiefs of Staff, John Shalikashvili, have written a "radical manifesto" which states that "the West must be ready to resort to a pre-emptive nuclear attack to try to halt the 'imminent' spread of nuclear and other weapons of mass destruction."

In other words, the generals argue that "the west" - meaning the nuclear powers including the United States, France and Britain - should prepare to use nuclear weapons, not to deter a nuclear attack, not to retaliate following such an attack, and not even to pre-empt an imminent nuclear attack. Rather, they should use them to prevent the acquisition of nuclear weapons by a non-nuclear state. And not only that, they should use them to prevent the acquisition of biological or chemical weapons by such a state.

Under this doctrine, the US could have used nuclear weapons in the invasion of Iraq in 2003, to destroy that country's presumed stockpiles of chemical and biological weapons - stockpiles that did not in fact exist. Under it, the US could have used nuclear weapons against North Korea in 2006. The doctrine would also have justified a nuclear attack on Pakistan at any time prior to that country's nuclear tests in 1998. Or on India, at any time prior to 1974.

The Nuremberg principles are the bedrock of international law on war crimes. Principle VI criminalises the "planning, preparation, initiation or waging of a war of aggression ..." and states that the following are war crimes:

"Violations of the laws or customs of war which include, but are not limited to, murder, ill-treatment or deportation of slave labor or for any other purpose of the civilian population of or in occupied territory; murder or ill-treatment of prisoners of war or persons on the seas, killing of hostages, plunder of public or private property, wanton destruction of cities, towns, or villages, or devastation not justified by military necessity."

To state the obvious: the use of a nuclear weapon on the military production facilities of a non-nuclear state will mean dropping big bombs on populated areas. Nuclear test sites are kept remote for obvious reasons; research labs, reactors and enrichment facilities need not be. Nuclear bombs inflict total devastation on the "cities, towns or villages" that they hit. They are the ultimate in "wanton destruction". Their use against a state with whom we are not actually at war cannot, by definition, be "justified by military necessity".

"The west" has lived from 1946 to the present day with a nuclear-armed Russia; no necessity of using nuclear weapons against that country ever arose. Similarly with China, since 1964. To attack some new nuclear pretender now would certainly constitute the "waging of a war of aggression ..." That's a crime. And the planning and preparation for such a war is no less a crime than the war itself.

Next, consider what it means to determine that a country is about to acquire nuclear weapons. How does one know? The facilities that Iran possesses to enrich uranium are legal under the non-proliferation treaty. Yes, they might be used, at some point, to provide fuel for bombs. But maybe they won't be. How could we tell? And suppose we were wrong? Ambiguity is the nature of this situation, and of the world in which we live. During the cold war, ambiguity helped keep both sides safe: it was a stabilising force. We would not use nuclear weapons, under the systems then devised, unless ambiguity disappeared. But the generals' doctrine has no tolerance for ambiguity; it would make ambiguity itself a cause for war. Thus, causes for war could be made to arise, wherever anyone in power wanted them to.

The generals' doctrine would not only violate international law, it repudiates the principle of international law. For a law to be a law, it must apply equally to all. But the doctrine holds that "the west" is fundamentally a different entity from all other countries. As the former Reagan official Paul Craig Roberts has pointed out, it holds that our use of weapons of mass destruction to prevent the acquisition of weapons of mass destruction is not, itself, an illegal use of weapons of mass destruction. Thus "the west" can stand as judge, jury and executioner over all other countries. By what right? No law works that way. And no country claiming such a right can also claim to respect the law, or ask any other country to respect it.

Conversely, suppose we stated the generals' doctrine as a principle: that any nuclear state which suspects another state of being about to acquire nuclear weapons has the right to attack that state - and with nuclear weapons if it has them. Now suppose North Korea suspects South Korea of that intention. Does North Korea acquire a right to strike the South? Under any principle of law, the generals' answer must be, that it does. Thus their doctrine does not protect against nuclear war. It leads, rather, directly to nuclear war.

Is this proposed doctrine unprecedented? No, in fact it is not. For as Heather Purcell and I documented in 1994, US nuclear war-fighting plans in 1961 called for an unprovoked attack on the Soviet Union, as soon as sufficient nuclear forces were expected to be ready, in late 1963. President Kennedy quashed the plan. As JFK's adviser Ted Sorensen put it in a letter to the New York Times on July 1, 2002:

"A pre-emptive strike is usually sold to the president as a 'surgical' air strike; there is no such thing. So many bombings are required that widespread devastation, chaos and war unavoidably follow ... Yes, Kennedy 'thought about' a pre-emptive strike; but he forcefully rejected it, as would any thoughtful American president or citizen."

It's not just citizens and presidents who are obliged to think carefully about what General Shalikashvili and his British, French, German and Dutch colleagues now suggest. Military officers - as they know well - also have that obligation. Nuremberg Principle IV states:

"The fact that a person acted pursuant to order of his government or of a superior does not relieve him from responsibility under international law, provided a moral choice was in fact possible to him."

Any officer in the nuclear chain of command of the United States, Britain or France, faced with an order to use nuclear weapons against a non-nuclear state would be obliged, as a matter of law, to ponder those words with care. For ultimately, as Nuremberg showed, it is not force that prevails. In the final analysis, it is law.