They 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.

(Click here to see a map of mass grave sites in Kosovo)

Lieutenant General Ruediger Drews, head of the German army's operational command, said: "We have extensive information on mass graves and the events at this time, although we are not sure all the details are exact."

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

The BBC's Jeremy Cooke: "The Nato troops were freeted by cheering ethnic Albanians"

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.

Helsinki agreement 'close'

As world leaders gathered in Cologne for a G8 summit, US President Bill Clinton said agreement was close over Russia's role in Kosovo.

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

The cost of rebuilding the province is also one of the priorities at the G8 meeting.

Talks continued through the night in Helsinki to work out the part Russia will play in the peacekeeping operation.

Russian troops are waiting to fly to Kosovo

Russian Defence Minister Igor Sergeyev and US Secretary of Defence William Cohen resumed their negotiations on Friday morning.

Moscow is still pressing for a separate Russian sector of control in Kosovo, but there appears to be a tentative agreement granting Russia a peacekeeping role in Kosovo, but within overall Nato command.

Nato forces are struggling to control the stream of Kosovo Albanian refugees heading back into the province.

The BBC's Peter Biles: "Nato troops ahead of schedule"

Despite pleas for refugees to wait until mines are cleared, thousands are continuing to head back, with Nato troops having trouble controlling the crowds.

Reports in the camps of Albanian looters crossing the border to ransack abandoned homes are giving many people a further sense of urgency.

(Click here to see a map showing timetable of Serb withdrawal and Nato's planned movements)

And as the Kosovo Albanians return, some 50,000 Serb families have fled the province, the World Food Programme (WFP) said.

In some cases the two streams of people are passing each other on the same narrow road.

{ Video 1}K-For Commander, Lieutenant-General Sir Mike Jackson, appealed for the Serbs to stay, insisting the peacekeeping force would protect them.

A WFP spokeswoman said most of the Serbian refugees were being looked after by communities in south-central Serbia.

Peacekeeping troops said on Thursday they had evidence that people were tortured at a Serb police headquarters in the capital, Pristina.

The International Criminal Tribunal for Former Yugoslavia in the Hague says it thinks ethnic cleansing in Kosovo was co-ordinated from the building.

• Clinton: US-Russia talks hopeful
• KLA move in
• Serb exodus unabated
• Serbs weigh Milosevic's policies
• Moderate Kosovar leader to return home

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