Nato officials have frankly admitted that the weather has significantly affected the alliance's air operations over Kosovo, and that they have so far not achieved as much as they might have wished.

Nevertheless, as the bombing enters its second week, key military figures insist that the Nato strikes are having a real impact on Yugoslav forces.

Nicholas Witchell: "Nato disappointed"

The alliance has announced that its warplanes and cruise missiles will now be taking in "high-value" targets throughout Serbia.

'Significant damage'

Even with the constraints of the weather, Nato has been doing some significant damage to fixed installations, such as headquarters, supply depots and airfields.

The impact on Yugoslav ground operations will be cumulative but with the weather set to improve, more strike aircraft available and the range of targets widened to include key military installations throughout Serbia, Nato promises a significant stepping-up of both the scale and scope of this operation.

The decision at the end of the first week of strikes to expand the air campaign represents the clearest signal yet that Nato is prepared to go as far as is necessary to keep up the pressure on President Slobodan Milosevic.

The fact that no Nato government dissented speaks volumes about the determination of the Alliance countries to weather any domestic opposition to their bombing campaign.

Indeed, as the scale of the catastrophe on the ground in Kosovo becomes clearer and the television images of refugees flooding across frontiers into neighbouring countries reach into peoples' homes, public opinion in the west is slowly shifting.

There is not by any means overwhelming public support for the air campaign. But Nato hopes that as the days go by more and more people will agree with its view that the Alliance had little choice but to act.

'Locked into a punitive strategy'

Batajnica airbase near Belgrade: A key target

Indeed some of the public concern probably reflects to the continuing fears - widely discussed by ex-military men and pundits in the western media - that air power alone may not be enough and that Nato ground troops may ultimately be needed.

With only a limited capacity to hit the actual units on the ground involved in the ethnic cleansing operations, Nato now seems locked into a punitive strategy.

Its aim is to hit as many important military targets in Serbia as possible - command centres, military industries, maybe even buildings like the Defence Ministry in Belgrade.

The assumption in Nato is that Mr Milosevic wants to retain an effective military machine - indeed the survival of his regime probably depends upon it.

Thus Nato believes that there is a level of damage that can be inflicted, beyond which Mr Milosevic will back down.

End-game changing

But there are also signs that the parameters of the end-game are changing.

Initially Nato's demand was that Mr Milosevic should sign the Rambouillet peace plan and grant Kosovo a three-year period of autonomy, after which its long-term future would be decided.

But the peace plan - accepted by the Kosovar Albanians - maintained Yugoslav sovereignty over Kosovo. There have been a number of hints from western leaders that the ethnic cleansing has changed the terms of the debate.

The German Chancellor Gerhard Schroeder has spoken of the need for a full withdrawal of Yugoslav army and special police units from Kosovo. The US President Bill Clinton has warned that Mr Milosevic might, by his actions, forfeit his claim to Kosovo.

Already in the corridors here at Nato an idea of one possible end-game is emerging.

'Digging in for the long-haul'

Significant damage: Barracks in Kragujevac, Serbia

According to this view Mr Milosevic would be forced to evacuate his forces from Kosovo. Some form of interim political arrangements would need to be put in place. And Nato troops would move swiftly into the vacuum to provide security and help rebuild Kosovo's shattered infrastructure.

This is not yet official Nato thinking. But there are clear signals that the Alliance believes that any settlement must go beyond the Rambouillet accord and that in the wake of the Yugoslav forces' sweep through Kosovo the ethnic Albanians can hardly be expected to accept the sovereignty of a man described by Nato as the "butcher of Belgrade".

Diplomatic insiders say that political cohesion in the Nato alliance is growing.