Moments after Nato's first air strikes on Serbia, Kofi Annan issued a statement, which was a model of balance for any diplomat required to tip-toe along a difficult tightrope.

He deeply regretted the rejection of a political settlement by Belgrade and emphasised that there were times when the use of force was legitimate in the pursuit of peace.

That pleased Nato's 19 member countries including three of the permanent members of the UN's Security Council - the United States, the United Kingdom and France.

But he went on to stress that the Council should have been involved in any decision to use force.

That kept him to the letter of the UN's Charter and mollified the two other permanent members of the Council, Russia and China, who would, if given the chance, have vetoed any military operation against Belgrade.

Talks offer

Mr Annan, has since offered to speak directly to the Yugoslav President Slobodan Milosevic to help bring an end to the crisis in Kosovo.

As the world's most senior diplomat, the secretary general clearly has a responsibility to give a moral lead at times of crisis.

But he also remains a civil servant who serves often divided masters. His careful use of language reflects this reality, as well as maintaining a degree of neutrality in case he is called upon to perform a role as a mediator further down the road.

He is no stranger to Nato or the Balkans. He has previously held the post of UN special envoy to Nato and was the head of the UN's peacekeeping operations during some of the worst years of the war in Bosnia.

The UN came in for criticism in Bosnia for not being "muscular" enough in its use of force, and not being prepared to point the finger at who they believed the true aggressors were.

Mr Annan acknowledged this in a speech last year when he said impartiality in performing a peacekeeping role was not the same as "an unthinking neutrality between warring parties".

'Deep distress' over refugees

In this conflict it is not difficult to see where the secretary general's heart lies.

The UN agencies, like the High Commission for Refugees, are in the forefront of coping with the flood of humanity crossing the Kosovo border into camps in Albania and Macedonia.

In a key statement issued last week Mr Annan talked of his "deep distress" and said "the suffering of innocent civilians should not be further prolonged."

He made demands not of Nato but of Belgrade. His requirement that Yugoslavia should withdraw its forces from Kosovo and accept the deployment of an international military force is broadly in line with Nato's stated aims.

If Slobodan Milosevic accepts Mr Annan's "good offices" he will have little doubt about what the secretary general's bottom line is.

Nato member countries have welcomed Kofi Annan's comments. But they are not playing up the idea that he might immediately enter the fray as a mediator shuttling back and forth between the sides.

Resistance to formal UN role

There is concern that a premature resolution could reward Slobodan Milosevic by enabling him to hold on to the gains his forces have made on the ground in Kosovo over the past fortnight.

Privately it is acknowledged that some Russian or Slavic involvement will almost certainly be necessary to make any future international force politically acceptable to the Serbs, but there remains resistance to a formal UN role in case that impedes the effectiveness of the force.

Last summer, Kofi Annan predicted some of the dilemmas now thrown up by the conflict in Kosovo when he said: "credible force without legitimacy (code for a Nato operation without UN approval) may have immediate results, but will not enjoy long-term international support."

On the other hand: "legitimate force without credibility (so often the case in underfunded, underarmed UN peacekeeping operations "may enjoy universal support but prove unable to implement the basic provisions of its mandate."

With Nato choosing to act without UN approval, Kofi Annan may appear to be on the sidelines.