When the initial shock of the terrorist attacks on the US had subsided and the official mourning period had passed, the thoughts of those people who witnessed and were affected by the atrocities understandably turned to retribution.Once those responsible had been putatively identified, in the shape of Osama Bin Laden and the al-Qaeda terrorist network, they were sought out for justice.

However, to some a manhunt and subsequent trial would not compensate for the loss of nearly 6,000 lives and there were calls for a more hawkish approach.

A large part of the American public, and others around the world, wanted an element of revenge in their justice.Here was a conundrum for the US, supported by the UK -- what action should they take to satisfy the public but stay within the parameters of international law?The approach the US has taken -- diplomacy followed by military strikes -- has been met with both approval and condemnation by international lawyers.The 'threat or use of force against the territorial integrity or political independence of any state' is prohibited by article 2(4) of the United Nations Charter, but there are exceptions.One of these is contained in article 51 of the charter, which states: 'Nothing .

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shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a member of the United Nations.'Malcolm Forster, joint head of the public international law g roup at City firm Freshfields Bruckhaus Deringer, says: 'The UK and US have set their military action in Afghanistan against this context of self-defence and I think it is a pretty clear-cut case.'This seems to be a view shared by the UN Security Council, for as Mr Forster points out: 'In a speech on 8 October, the Secretary General of the UN, Kofi Annan, stopped short of endorsing the air strikes but acknowledged that states have a right to individual and collective self-defence.'The anomaly in this particular case, of course, is that it was not actually Afghanistan that carried out the attacks in New York and Washington -- but allegedly the al-Qaeda organisation.Jeremy Carver, head of the international law group at Clifford Chance, says that because the Taliban are allowing Mr Bin Laden to carry on his activities in Afghanistan, they are culpable of wrong-doing.

'Essentially, the international world is made up of borders defined by states and not governments,' he says.

'Therefore, states are responsible for everything and everybody within these borders.'He continues: 'The state of Afghanistan has said that the coalition shall not have access to the prime suspect to the atrocities.

In order to fulfil the aim of extracting the culprits, it is necessary to knock out the air defence system of the Taliban, and thus force may be used under article 51.

The bombing is the most appropriate way of dealing with the situation.'Alan Perry, an international law partner at City firm DJ Freeman, concurs.

He says: 'Essentially, by harbouring al-Qaeda, the Taliban are harbouring a threat to US citizens.' This raises the question whether the UK can justify its involvement, but Mr Perry says: 'The attacks on 11 September can be classed as an attack on the nationals of the UK, as a number of them perished.

Any sensible court would thus accept the argument that the UK can join the US in exercising collective self-defence.'However, article 51 states that self-defence can only be exercised in the face of an 'armed attack' and it is difficult to class the attacks by al-Qaeda as such.

Even so, case law on this matter seems to support the actions of the coalition -- an example being the Cuban missile crisis in 1962.The US government imposed quarantine against Cuba in response to its importation of offensive nuclear weapons from the Soviet Union -- justifying its actions as a form of self-defence.The Soviet Union had never asserted a military presence of such a magnitude in that area before and by doing so it was cutting the US reaction time to military attack from six or seven minutes to three.

It was thus concluded that the action of the US was lawful as the operations of the Soviet Union created reasonable apprehension of imminent danger to the territorial integrity and political independence of the US.On this basis it seems likely that the attacks on 11 September present a 'reasonable apprehension of imminent danger' and even though not an actual 'armed attack', constitute enough of a threat to invoke self-defence.Mr Perry says the common test for lawfulness concerning the actual self-defence is that the response is 'necessary and proportionate'.

The sanctions imposed in the Cuban missile crisis were held to be proportionate, but the bombing of a state and the potential loss of civilian lives is more contentious.Mr Perry says: 'Article 51 (4) of the 1977 Geneva Convention (for the protection of victims of international armed conflicts) prohibits indiscriminate bombing, which article 51(5)b defines as "an attack which may be expected t o cause incidental loss to life, injury to civilians .

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which would be excessive in relation to the concrete and direct military advantage anticipated".''I don't personally think the action against the Taliban is a blatant breach of the convention, but it could be argued that the intentions of the bombing are not purely military.'Mr Forster points out that military action is also authorised under Chapter VII of the UN Charter in response to threats to international peace and security.

'The Security Council has identified terrorism as presenting such a threat,' he says.'The drafting of the charter makes it clear that, although other measures are envisaged such as sanctions sit is not essential to try these first if they would be inadequate.'This seems to support the air strikes, as it is highly unlikely that sanctions would have the desired effect on terrorism or remove the immediate threat posed by al-Qaeda.Of course, self-defence is not the only reason for taking military action and there have been examples in recent history of other exceptions to article 2(4) and the legitimate use of force against other states.Mr Forster explains: 'The liberation of Kuwait was achieved by a UN coalition acting on a Security Council resolution in the face of a clear case of mis-use of force by Iraq.'He continues: 'The recent operations in the Balkans are a more difficult case, but I imagine the UN peace-keeping force can justify its intervention on humanitarian grounds.'Since the UN Charter was signed in 1945, it has been the yardstick by which all international conflicts have been measured and it has been effective in its function to varying degrees.'There was initial optimism after the Second World War at the establishment of a new world order,' says Mr Carver.

'However, this started falling apart in a matter of years due to the Cold War making it impossible to avoid inevitable clashes.'The UN response to the Kuwait situation gave new hope that there was finally a body which could act on behalf of the international community.

However, this was fraught with difficulties and further uses of force in Somalia, the Balkans and Libya drew us back towards the dark days -- epitomised by the further bombing of Iraq in 1998.'Mr Carver hopes recent troubles will lead to 'the world shaking itself down and international states taking responsibility for themselves'.This raises the question -- what next? There has been talk of launching further attacks on Iraq under the same premise as the strikes on Afghanistan, but most international lawyers unanimously condemn this.Mr Forster says the Security Council would never endorse further strikes on Iraq, and Mr Carver echoes this view.

'Unless you can show that Iraq plans an attack, it would definitely be deemed over-aggressive.'Terrorism is a multi-headed hydra with bases all over the world.

The aim must be to cut off the principal body -- al-Qaeda -- and hope the other heads die.'With new non-permanent members set to join the Security Council at the end of the year, the issuing of resolutions and the council's endorsement of military action will, according to lawyers, undoubtedly change.'The new members in 2002 are Bulgaria, Cameroon, Guinea, Mexico and Syria,' says Mr Forster.

'These could all be classed as non-western, non-capitalist states and may thus have greater sympathy towards those opposed to the west.'This could indeed give rise to situations where the Security Council does not back strikes against countries harbouring religious extremists in the Middle East, though as Mr Forster says: 'Hopefully these circumstances will never happen again.'