A Nato official in Belgium said alliance ambassadors had decided that military reconnaissance teams would leave for 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.

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.

Thousands flee to Albania

Many people have abandoned their homes

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 up to 5,000 are estimated to have fled into neighbouring Albania. Thousands more reported to be hiding in hills in western Kosovo.

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.