About 5,000 have arrived in neighbouring Albania with nearly as many reported to have gone to Montenegro, Yugoslavia's smaller republic.

Ethnic Albanian refugees arrive in Albania after fleeing the fighting

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.

Entire villages have been destroyed in an area near the border with Albania which remains closed to the outside world. There are reports of some summary executions.

For the past five days, Serbian forces have been targeting several ethnic Albanian villages west of the provincial capital, Pristina.

Nato believes Serb forces are trying to cut off guerrillas of the Kosovo Liberation Army from their safe haven and source of supplies in Albania by clearing and occupying a swathe of land on the border. About 40 ethnic Albanians and two Serbian policeman have been reported killed.

Nato acts Kosovo

Earlier, Nato decided to speed up moves to help Albania and Macedonia seal their borders with Kosovo.

Military commanders are preparing contingency plans to deploy up to 23,000 soldiers to guard Albania's borders but won't report for some weeks.

A Nato official in Belgium said alliance ambassadors had decided to send military reconnaissance teams to the two countries within hours.

The official said there would be no immediate decision on whether to deploy troops in the region.

Fear of a "second Bosnia"

Nato spokesman Jamie Shea: "NATO has learned the Bosnia lessons rather well"

Nato spokesman, Jamie Shea, 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 rejected allegations by Albania that Serb security forces were carrying out an "ethnic cleansing" campaign in Kosovo.

Many people have abandoned their homes

The specific details of the operation will be presented to Nato Defence Ministers when they meet next week but the Nato spokesman said the planning stage could not be rushed and that Nato needs "a few days to complete the planning process".

He added that the ambassadors were determined Kosovo should not become a second Bosnia, as he put it, with the international community doing too little too late.

But the BBC correspondent in Brussels, David Eades, says that even as Nato insists no option has yet been ruled out, there is clearly no great willingness within the alliance to take such a bold step.