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Nato has announced a major operation to save the lives of thousands of refugees who have fled Kosovo.

It is establishing a field headquarters in Albania, staffed by up to 8,000 troops, which will help ferry aid to more than 150,000 Kosovo Albanians.

But as refugees continue to pour out of Serbia, Macedonia says it cannot take any more people.

The government has announced it will only let in refugees who have guaranteed passage to other countries.

The move leaves an estimated 50,000 people stuck at the Blace border post in freezing temperatures.

At least 11 people, including four babies, have died since Friday night. Reports say disease is spreading and there have been fights for what little food there is.

Ben Brown on the Kosovo-Macedonia border: "Disease is spreading and people are dying"

Some refugees have threatened to march out of the camp into Macedonia.

But security forces are standing by in riot gear with automatic weapons to prevent any unauthorised movements from the border area.

Sanctuary plan

Britain has put forward a plan for the creation of a Nato-protected refugee sanctuary inside Macedonia - which could enable it to re-open its borders.

UK Foreign Secretary Robin Cook said he had begun talks with Macedonia, Nato and the United Nations High Commissioner for Refugees (UNHCR).

"The proposal has been greeted with interest by the Macedonian Government," he said. "It would be jointly run by Nato and the UNHCR. Food, blankets and medicines would be supplied by a Nato air bridge into Macedonia.".

The UNHCR estimates 170,000 people have fled or been expelled to Albania and 115,000 to Macedonia since 24 March.

But some aid agencies have accused Macedonia of deliberately hampering the flow of refugees. One British charity, Children's Aid, is leaving Macedonia and taking its food supplies to Albania in protest at the obstructions.

Germany: We'll take refugees

About 315,000 Kosovo Albanians have poured out of Kosovo since the air strikes began. Nato says at this rate the Serbs will empty their southern province within another 20 days.

A sick refugee in Blace is carried on a makeshift stretcher

Germany has said it will start daily airlifts to refugees in Albania and Macedonia and the United States says it is sending food, tents, sleeping bags, cots and trucks.

Chancellor Gerhard Schröder also said Germany was ready to take some of the refugees on a temporary basis and appealed to other European states to share the burden.

British pledge

UK Prime Minister Tony Blair warned Yugoslav President Slobodan Milosevic on Saturday that Nato would reverse the expulsion of Kosovo's Albanians.

In a pledge to the refugees, he said: "We will not let you down. We will make sure that you are able to return to your homes, and live in your homes in peace. That is our promise to you and we will carry it out."

President Clinton: "One in three have been made homeless"

Speaking in his weekly radio address to the American people, President Bill Clinton said: "We can't end all suffering, we can't stop all violence.

''But there are times when looking away simply is not an option. Our goal is to exact a very high price for Mr Milosevic's policy of repression."