Western powers have justified military action over Kosovo by citing the need to prevent a humanitarian catastrophe.

The UN Security Council has, in the past, stressed the need to prevent such a catastrophe and demanded that the Belgrade authorities stop repression of civilians in Kosovo.

During the abortive peace talks in Paris, President Milosevic was warned that if he did not accept the international plan signed by the Kosovo Albanians, air strikes against Serb targets would follow.

But now western officials say the primary purpose of air strikes is not to compel him to sign.

Defiant Milisav Paic is the Yugoslav deputy ambassador to Britain

The argument is rather that the consequences of doing nothing are so appalling in terms of human suffering that action must be taken.

There is some support for this in past UN Security Council resolutions.

No direct backing for strikes

The most explicit (SCR 1199 of 23 September 1998) emphasises the need to prevent a humanitarian catastrophe in Kosovo.

A Tornado aircraft being prepared for action

It demands that Yugoslavia should stop the repression of civilians and identifies the situation in Kosovo as a threat to regional peace and security.

The security council resolutions were passed under Chapter VII of the United Nations Charter, which provides for possible action to enforce them.

But they do not authorise Nato or anyone else to take military action.

European members of Nato do point to the indirect backing for action in Kosovo which they deduce from security council resolutions.

The United States, on the other hand, argues that no such justification is needed. It says Nato itself has the right and authority to act to prevent a humanitarian disaster and a threat to stability throughout the Balkans.

Nato's role expands

Nato was set up to defend the territory of its members from attack. But in recent years it has been extending the scope of its influence and action more widely.

Kosovo Albanian refugees: Human suffering

It has accepted new members and drawn up a Strategic Concept that identifies threats to the Alliance from various sources, including ethnic rivalries and territorial disputes in eastern Europe.

Russia is jealous of what it sees as Nato's aggrandisement, and together with China, insists on preserving the unique prerogative of the Security Council to authorise the use of force.

That means that in practice no authorisation will be given.

Grey area

The legal authority for air strikes is not clear-cut. It is a grey area of international law which if anything is getting greyer.

But the argument of western politicians is moral and political. They rely on the overriding obligation to stop the suffering of innocent civilians and prevent a de-stabilising conflict spreading to other countries in south-east Europe.