Nato ambassadors are meeting in Brussels to "review military preparations" decided last week by foreign ministers for possible troop deployments in Albania and Macedonia in case the Kosovo conflict spreads.

Nato spokesman James Shea: "We are determined to prevent the spill over of the conflict."

Nato officials say they want to send a very clear message to Yugoslav President Slobodan Milosevic not to attempt to destabilise the situation in neighbouring countries.

Military planners are looking at how a new force of up to 25,000 troops could be deployed along Albania's border with Kosovo.

It would serve a dual function - to stop Serbian forces pursuing Kosovan Albanians across the border, and to seal off the flow of weapons from Albania into the province.

But the plans are not yet complete, and the BBC Brussels correspondent says there is little willingness among NATO countries to go that far.

Defence ministers of the alliance are due to meet in Brussels on June 11 to discuss the next step.

A Nato spokesman said the alliance was extremely concerned, and civilians were increasingly the victims of an apparent Serbian policy to clear out areas near the Albanian border.

But the official rejected allegations by Albania that Serb security forces were carrying out an "ethnic cleansing" campaign in the rebellious ethnic Albanian-majority province.

Ethnic Albanian refugees arrive in Albania after fleeing the fighting

The moves follow a five-day security operation by Serbian forces against several ethnic Albanian villages west of the capital, Pristina.

At least 20 ethnic Albanians are said to have been killed and about 2,000 have fled into neighbouring Albania.

General Wesley Clark, Nato Supreme Allied Commander in Europe, has said there are growing reports of the use of artillery and heavy weapons by the Serbs.

Serbs accused

The Albanian Prime Minister, Fatos Nano, has accused Serbia of "ethnic cleansing" and warned that Albania might toughen its stance on the dispute.

Paul Wood reports on the exodus of refugees

The situation for refugees fleeing the fighting in the Serb province of Kosovo is deteriorating rapidly, according to another UN spokesman.

At least 2,000 people have crossed into neighbouring Albania to escape from an offensive by Serb forces against ethnic Albanian guerrillas.

Thousands more are reported to be hiding in hills in western Kosovo.