Any act of reprisal by the US government for last month's attack on America could constitute a war crime, according to the director of the Irish Centre for Human Rights at NUI Galway, Prof William Schabas.
Prof Schabas, an expert in international law from Canada who has worked in the former Yugoslavia and Rwanda, has said that the anger of the victims and their families can well be understood. However, the attacks were not a threat to democracy, he says.
"Democratic regimes have survived far worse. It is the reaction to terrorism that destroys democracies.
"Some American politicians now argue that criminal justice is inadequate because the events of September 11th were 'an act of war' ", he has noted. "But according to international law, we must know what state committed it. A group of individuals, even numbering in the hundreds, cannot commit an 'act of war' ".
The Galway-based academic made his comments as he prepared to host a conference in NUI Galway last week on international abolition of the death penalty.
"Modern democracies have perfectly adequate justice systems for dealing with terrorists," he emphasised. "We track them down, catch them, bring them to trial and impose fit punishment.
"That is what the US and Britain did with those responsible for the Lockerbie crash, and for the US embassy bombings in Nairobi, Kenya, and Dar es Salaam, Tanzania. It is what the United Nations is doing for those accused of genocide and crimes against humanity in the former Yugoslavia and Rwanda.
"How much more healthy it is for democracy that Slobodan Milosevic, the former Serbian leader, be judged by an international court rather than murdered by a Cruise missile aimed at his home. As for the two Lockerbie defendants, one was acquitted by Scottish judges earlier this year. Had the advocates of assassination and summary execution prevailed in that case, an innocent man would have been killed in the name of democracy's war on terrorism."
He added: "Perhaps those who harbour terrorists may themselves be accomplices in an 'act of war'. But let us remember the last time this bold claim was made, in 1914, when Austria-Hungary declared war on Serbia because a Serb nationalist had assassinated its archduke. It unleashed a cascade of belligerent declarations justified by an earlier equivalent of article five of the NATO treaty.
"We now look back in horror and bewilderment at how an overreaction to terrorism, in the name of punishment and retribution, provoked a chain of events that ultimately slaughtered an entire generation of European youth." Any act of reprisal that took civilian casualties or was directed against civilian objects was forbidden under international law, he said. "It is a war crime. To the extent that reprisals are allowed at all, they must target purely military objectives."
International solidarity should not become "a pretext for promoting a US political agenda that has little to do with catching the perpetrators and preventing future crimes," he said. "The right to life of thousands of innocent civilians in New York city and Washington has been egregiously violated. But that same right also belongs without exception to civilians in Belgrade, Baghdad and Kabul."