A British team of forensic experts will arrive on Saturday, to be joined the following day by American, French and Canadian scientists.

The teams hope to reach as many sites as possible before returning refugees arrive and disturb evidence.

As soon as troops have secured areas and cleared them of mines, the investigators will begin work, collecting surface evidence such as bullet cases and skull fragments.

The locations of 50 alleged mass graves were revealed at a briefing by the UK Ministry of Defence on Friday.

New Nato powers

The BBC's Craig Swan: "The smell is quite gagging"

Nato troops have been granted new powers to take an active role in bringing suspected war criminals to justice under an agreement between allied nations and the international tribunal.

K-For troops will take a "considerably more proactive stance in supporting the efforts of the Tribunal, including if need be on apprehension issues," Judge Louise Arbour, chief prosecutor of the International Criminal Tribunal, told a news conference at Nato's headquarters in Brussels on Friday.

She said K-For's role in dealing with suspected war criminals would be "considerably different" to that of the Nato-led force in Bosnia which has been strongly criticised for not detaining Serb leader Radovan Karadzic and others indicted for war crimes.

Canada's Defense Minister Art Eggleton, who also attended the news conference, said a six-member contact group would ensure liaison between K-For and the tribunal.

Louise Arbour said it was essential the experts began work swiftly to prevent "extensive contamination" of the evidence.

"We have several sites prioritised for immediate attention. We are also obviously concerned ... that we may have to address other sites. Some of them have been brought to our attention by K-For," she said.

Massacres

In London, the UK Foreign Office said according to refugee reports about 10,000 people had been killed in more than 100 massacres.

Nato forces have been gathering evidence of the atrocities as they spread out into the province, with British troops pushing into the north of the province days ahead of schedule.

Serb forces in the north still have some days to withdraw, but the deadline for those stationed in central Kosovo is midnight on Friday.

Nato says it is to send 50 tanks and armoured vehicles to help maintain law and order in the Kosovan capital, Pristina.