Since Guantanamo Bay is technically foreign territory, the detainees have no rights under the US constitution and cannot appeal to US federal courts. Any rights they might have under international law have been firmly denied. According to Rumsfeld, the detainees "will be handled not as prisoners of war, because they are not, but as unlawful combatants".

This unilateral determination of the detainees' status is highly convenient, since the 1949 Geneva convention on the treatment of prisoners of war stipulates that PoWs can only be tried by "the same courts according to the same procedure as in the case of members of the armed forces of the detaining power". The Pentagon clearly intends to prosecute at least some of the detainees in special military commissions having looser rules of evidence and a lower burden of proof than regular military or civilian courts. This will help to protect classified information, but also substantially increase the likelihood of convictions. The rules of evidence and procedure for the military commissions will be issued later this month by none other than Donald Rumsfeld.

The Geneva convention also makes it clear that it isn't for Rumsfeld to decide whether the detainees are ordinary criminal suspects rather than PoWs. Anyone detained in the course of an armed conflict is presumed to be a PoW until a competent court or tribunal determines otherwise. The record shows that those who negotiated the convention were intent on making it impossible for the determination to be made by any single person.

Once in front of a court or tribunal, the Pentagon might argue that the Taliban were not the government of Afghanistan and that their armed forces were not the armed forces of a party to the convention. The problem here is that the convention is widely regarded as an accurate statement of customary international law, unwritten rules binding on all. Even if the Taliban were not formally a party to the convention, both they and the US would still have to comply.

The Pentagon might also argue that al-Qaida members were not part of the Taliban's regular armed forces. Traditionally, irregulars could only benefit from PoW status if they wore identifiable insignia, which al-Qaida members seem not to have done. But the removal of the Taliban regime was justified on the basis that al-Qaida and the Taliban were inextricably linked, a justification that weakens the claim that the former are irregulars.

Moreover, the convention has to be interpreted in the context of modern international conflicts, which share many of the aspects of civil wars and tend not to involve professional soldiers on both sides. Since the convention is designed to protect persons, not states, the guiding principle has to be the furtherance of that protection. This principle is manifest in the presumption that every detainee is a PoW until a competent court or tribunal determines otherwise.

This too is the position of the International Committee of the Red Cross, which plays a supervisory role over the convention. The Red Cross and Amnesty International have both expressed concerns over the treatment of the detainees.

The authorities at Guantanamo Bay have prohibited journalists from filming the arrival of the detainees on the basis that the convention stipulates PoWs "must at all times be protected against insults and public curiosity". The hypocrisy undermines the position on PoW status: you can't have your cake and eat it.

Even if the detainees were not PoWs, they remain human beings with human rights. Hooding, even temporarily, constitutes a violation of the 1984 convention against torture and cruel, inhuman or degrading treatment. Apart from causing unnecessary mental anguish, it prevents a detainee from identifying anyone causing them harm. Forcefully shaving off their beards constitutes a violation of the right to human dignity under the 1966 international covenant on civil and political rights. Forcefully sedating even one detainee for non-medical reasons violates international law. Although strict security arrangements are important in dealing with potentially dangerous individuals, none of these measures are necessary to achieving that goal. If human rights are worth anything, they have to apply when governments are most tempted to violate them.

There are many reasons why these and other violations are unacceptable. The rights of the detainees are our rights as well. Yet international law can be modified as a result of state behaviour. If we stand by while the rights of the detainees are undermined, we, as individuals, could lose.

British and American soldiers and aid workers operate around the world in conflict zones dominated by quasi-irregular forces. The violations in Guantanamo Bay will undermine the ability of our governments to ensure adequate treatment the next time our fellow citizens are captured and held. Respecting the presumption of PoW status and upholding the human rights of detainees today will help to protect our people in future.

The US has occupied much of the moral high ground since September 11, and benefited enormously from so doing. Widespread sympathy for the US has made it much easier to freeze financial assets and secure the detention of suspects overseas, as well as secure intelligence sharing and military support. The sympathy has also bolstered efforts to win the hearts and minds of ordinary people in the Middle East, south Asia and elsewhere. That might just have prevented further terrorist attacks.

Ignoring even some of the rights of those detained in Guantanamo Bay squanders this intangible but invaluable asset, in return for nothing but the fleeting satisfaction of early revenge. The detainees should be accorded full treatment as PoWs and, if not released in due course, tried before regular military or civilian courts - or even better, an ad hoc international tribunal. As the world watches, vengeance is ours. But so, too, are civilised standards of treatment and justice.

· Michael Byers teaches international law at Duke University, North Carolina. He is currently a visiting fellow at Keble College, Oxford.