The slaughter of thousands of innocent civilians in New York, Washington and Pennsylvania is a truly atrocious crime.

The appalling truth is this was an act of audacious simplicity: Seemingly, four teams of three men apiece, armed with knives and airline timetables, prepared to kill themselves along with others in order to strike a symbolic blow at American power.

To cause this devastation required organisation - intelligence, imagination and supreme dedication rather than investment of large amounts of money or sophisticated weapons. It could not be clearer how vulnerable our complex societies are to small groups of terrorists.

President George W Bush says: "The US will hunt down and punish those responsible." Truly, the only answer to such wanton lawlessness is international justice. But this means the enforcement of law, through the identification, arrest and trial of all those found to have been responsible for these crimes against humanity.

This was how Serbian General Krstic was recently condemnned by the International Tribunal for the massacre (of a comparable order) at Srebrenica in 1995 and how Timothy McVeigh was condemned for the Oklahoma bombing. Any governmental leaders who can be shown to be involved should also be put on trial, like former Serbian president Slobodan Milosevic, and political measures taken against their regime by the United Nations.

However, it is no answer for President Bush to launch military strikes against Afghanistan or any other country suspected to be supporting anti-American terrorists. This is true even if it can be shown they were in some way linked to this attack. Any strikes of the kind President Clinton launched previously against Afghanistan and Sudan will serve a purely propaganda purpose. They will not stop terrorists organising. They will almost certainly kill innocent men, women and children along with fighters. The families of Islamic militants do not deserve to die any more than the secretaries of American generals in the Pentagon.

The terrible truth is that people are only prepared to kill themselves for strongly held beliefs fuelled by a deep sense of injustice. If, as seems likely, they were Arab militants, their motivations must include the anger over longstanding US support for Israeli power.

It may be a little too simple to say the US is paying the price for Ariel Sharon and for Bush's willingness to see the last vestiges of the peace process disappear in the blood of Palestinians and Israelis, but the longer failure of US policy in the Middle East cannot be taken out of the equation. The atrocity in the US is the most shocking single incident in a long trail of blood, which has, until now, been spilt elsewhere in the world.

We need to stop the round of slaughter. This will need new policies from the US and world leaders, not the reinforcement of old policies by the discredited methods that all too probably played their part in bringing devastation to downtown Manhattan.

-Martin Shaw, Professor of International Relations, University of Sussex