THERE IS A NEW RULE when taking on the bad guys now that the winds of the war on terrorism are blowing with typhoon strength - anything goes. That was exactly the maxim the battle-weary humanitarians who drew up the Geneva Conventions in the wake of World War II wanted to avoid. They had just suffered six years of the bloodiest mayhem humankind had endured - genocide, atomic bombs, crimes against humanity of the most heinous magnitude - and wanted no more. Ever. In seeking to ensure the death of such evils, they drew together regulations and protocols that had been observed by warring nations since the 19th century, amending and adding to reflect their experiences. Their labours culminated in the first four conventions; a code of conduct dealing with combatants, weapons, prisoners of war and excessive use of force, which were approved by a diplomatic conference on August 12, 1949. Protocols have been added and altered when necessary. Then came September 11. With the collapse of New York's twin towers came US President George W. Bush's urgency for revenge. With the best of Wild West logic, he sent out the posse. No cowboy is ever known to have kept a copy of the Geneva Conventions in his saddlebag. But do not accuse the Bush administration of not playing by the rules. They say that the US is under attack and that they have the legitimate right to go anywhere and do whatever is necessary to eliminate the threat. Enter the weapons inventors of the 21st century, who grew up on Star Wars and in between creative bursts, blast away the baddies with death rays and laser swords in computer games like Battle Realms and Starcraft. Their genius had to be admired last Sunday when six suspected members of the al-Qaeda terrorist group were blown to pieces when a rocket from an unmanned US drone slammed into their car in the remote Yemen province of Marib. Among them was apparently Qaed Senyan al-Harthi, a suspect in the killing of 17 US sailors in the bombing two years ago in Aden of the US destroyer Cole. Technological brilliance aside, the incident raises serious questions. Should not Harthi, a suspected criminal, have faced a judge instead of the blast of a missile? What authority does the US have to carry out what some would term terrorism in a foreign country? How can a nation, which admonished Israel for firing a missile into a building in the West Bank which killed a high-ranking Palestinian militant and a dozen innocent civilians, so brazenly carry out a similar act just months later? By ignoring international law, said US legal expert Ved Nanda. Neither did he believe that invoking Article 51 of the United Nations Charter - the right to use pre-emptive self-defence - was justification. 'It opens a Pandora's box,' he said. 'Once you start moving in that direction, it is a slippery slope. If you think about humanitarian law or the laws of war, it would be very hard to justify that kind of an action.' The legal framework had been clear until September 11, when non-state terrorists such as al-Qaeda became the focus of international attention. The laws were shown to be incapable of dealing with such problems. Professor Nanda, the director of University of Denver College of Law's international legal studies programme, said the Geneva Conventions needed updating by adding a treaty on dealing with the use of force against non-state combatants. But some security analysts do not see a problem. Daniel Benjamin, a senior fellow at the Washington-based Centre for Strategic and International Studies and co-author of Age of Sacred Terror, said the casualties inflicted on September 11 were on the scale of a war and the US response was therefore acceptable. 'Since we've seen that terrorists can create casualties on the scale of a war, the US is going to take the position that these are combatants and it is effectively a war even if the terrorists don't have a country of their own,' he said. 'In such circumstances where they can't be captured and brought to trial, then this is an acceptable tactic.' It is now a moot point whether Harthi and his travelling companions could have been captured. Yemen's central government does not control the whole country and, as a result, it would have been difficult for the US to send a team to arrest them. There would probably have been a high degree of risk in such an operation. The missile attack was also not the first of its kind carried out by the US. US missiles were fired at terrorist camps in Afghanistan and a chemical plant in Sudan in 1998 after the bombings on American embassies in East Africa. In both cases, the concept of pre-emptive self-defence was used. The relatives of the estimated 4,000 civilian victims of US bombing raids in Afghanistan would say otherwise. There is clearly a divergence in opinion and an urgent need to review the rules of warfare. The war on terrorism is a necessity and its targets must be wiped out. But in the process, basic human rights and civil liberties cannot be trampled and ignored. Peter Kammerer is the Post's foreign editor. This column will appear regularly on the Analysis page