Nato's message to the warring parties in Kosovo is blunt and to the point. There is now an internationally backed proposal for negotiations on an interim peace deal for the troubled province.

It is an offer that both sides should seize and seize quickly and if there is no progress, if the offer is rejected or if hostilities continue on the ground, then Nato air power will be ordered into action.

The alliance's Secretary General, Javier Solana, now has the authority to give that order.

BBC World maps out Nato's military options

Meanwhile, Nato is developing alternative plans, in the event that talks do result in an interim settlement, and its troops are required to keep the peace.

Somewhere between 20,000 and 30,000 Nato troops might be required to keep the peace in Kosovo during any interim political settlement.

But Nato has made clear that its troops will only go into Kosovo once a peace deal is accepted by all sides.

The threat of force

Some 200 war planes are on stand-by and Mr Solana says he has been authorised if necessary to launch air strikes on the targets on the territory of the federal republic of Yugoslavia, emphasising that Nato military action might be broad in scope and not confined to targets in Kosovo itself.

But the actions of the Kosovo Albanians would also be considered before launching any attack.

Nato is clearly struggling to find ways of persuading the separatist Kosovo Liberation Army to suspend its operations. Continued fighting on the ground would undermine the whole negotiating process.

Last October Nato came to the brink of launching attacks against Serbian forces in Kosovo. But despite the strong Nato rhetoric, uncertainties about such action remain in the back of many people's minds.

There is no doubt that Nato is quite capable of unleashing a punitive and damaging attack against President Slobodan Milosevic's forces in Kosovo.

Plans for such an air campaign were all in place last October. And a force of nearly 400 aircraft from several countries had been assembled in Italy.

The 200 currently on alert at Nato bases facing the former Yugoslavia across the Adriatic could be rapidly reinforced.

Cruise missiles could also be used, fired from US warships patrolling in the Adriatic. The only limiting factor on Nato's actions would be the need to withdraw all of the unarmed OSCE monitors from Kosovo in advance of any military action.

A French-led force of Nato troops stands ready in Macedonia to extricate the monitors if they get into trouble, but if they all had to be got out this force would require significant reinforcement.

A phased air campaign would hit fixed Yugoslav army installations - missile sites, command centres and supply dumps, and it could go on for several days if President Milosevic failed to bow to Nato's demands.

Clearly air defence sites would be among the initial targets; but the initial attacks could be limited, with Nato ratcheting up the pressure as the campaign went on.

'When the smoke clears'

But the Alliance knows that this is a high-risk strategy. The ethnic Albanian separatist movement - the KLA - might well seek to take advantage of the Nato air strikes to step-up its own activities against Serbian forces. Nato is not seeking to go to war with Slobodan Milosevic, but to pressure him to give way.

Tens of thousands have been made homeless since the offensive began

It is an uncertain and unpredictable strategy. And the real dilemma facing Nato is not so much the launching of air strikes, but what would happen next once the smoke clears.

If some semblance of order were to be restored in Kosovo an armed international presence might well be needed on the ground. That means Nato combat troops. They could be in Kosovo for a very long time.

It is something Nato leaders do not want to think about for now, but Alliance ambassadors know that air strikes without some long-term strategy would make little sense.

Keeping the peace

If a settlement does emerge from the talks, Nato realises that, while any force it deploys might be scaled down over time, it will probably have to remain in Kosovo for anything between three and five years.

A key factor will be the exact wording of any peace deal. The Dayton agreement on Bosnia contained a powerful annexe giving Nato-led troops considerable freedom of action.

Nato commanders would like similar undertakings to be written into any Kosovo deal.

The Americans want a smaller commitment than they had under the Dayton process. They know that to some extent they can trade absolute numbers on the ground against logistical and intelligence support.

Command of any operation would be given to the Nato Rapid Reaction Corps which is headed by a British officer, but ultimate command would be vested in the Supreme Allied Commander Europe who is an American.