Defence Secretary William Cohen signed an order in Washington sending 12 Air Force F-117 stealth fighter-bombers, 10 Navy EA-6B electronic warfare planes and 29 refuelling planes to a base in Europe.

The deployment brings to 260 the number of US aircraft which could be used in Nato air strikes against Serbian targets. The forces are on 48-hour alert.

Bridget Kendell: "Time is running out"

Defence spokesman Kenneth Bacon said the action was being taken in case the Serbs blocked a deal at the peace conference in France.

The Serbs oppose the deployment of a Nato-led military force to implement any peace deal as they say it would deny their sovereignty.

The international plan calls for a cut in Yugoslavia's forces in Kosovo

The US spokesman said the planes would move "in the next couple of days". However he did not specify where they would be sent.

The move followed fresh US warnings against Serbia. State Department spokesman James Foley said Yugoslav President Slobodan Milosevic had only a few days "to see the light".

The Clinton administration has warned that the Serbs could face swift and severe consequences if their position does not change by noon on Saturday - the deadline for the end of the peace talks.

Diplomats say the chances of agreement are less than 50%. Aside from the Serbs' intransigence, the ethnic Albanians - who account for 90% of Kosovo's population - have rejected international calls to disarm.

The scene of the talks - less than 50% chance of success

UK Foreign Secretary Robin Cook and his French counterpart, Hubert Vedrine, have called for a redoubling of effort on both sides in order to meet the deadline.

After meeting the international negotiators and both delegations at the talks at Rambouillet near Paris, the two men said there was some movement.

However BBC Diplomatic Correspondent Barnaby Mason said progress seemed to be confined to the political parts of the proposed peace settlement - dealing with the constitution and institutions of a self-governing Kosovo during an interim period of three years.

Barnaby Mason: "This is the first positive outcome in recent days"

Mr Cook said the co-chairman of the talks hoped that an agreement on the broad principles of the political text could be achieved in the very near future.

He said instructions had clearly been given to the Serb delegation from Belgrade and the Serb delegation was engaged in the negotiations.

One of the leaders of the Serb delegation, Nikola Sainovic, flew home this week to confer with President Milosevic. Together with a brief visit by the chief American negotiator to Belgrade, it confirmed the importance of Mr Milosevic's involvement, despite Kosovo Albanian displeasure at negotiations taking place elsewhere.

Conference sources said the two delegations at Rambouillet did meet for five minutes on Wednesday, though a joint negotiating session did not take place.