The new allegations came as senior diplomatic sources said there were reliable reports that Serbian mass executions had taken place in 75 towns and villages across the province, including the Drenica region and the town of Malisevo.
The allies now have a firm tally of 5,000 murdered Albanians, although this figure is thought to be a gross underestimate of the true scale of the atrocities. As many as 225,000 men from Kosovo are unaccounted for.
According to Nato, Serb forces are now making great efforts to hide evidence of the death toll, reburying bodies in individual graves at sites bombed by Nato or in areas formerly occupied by the Kosovo Liberation Army.
Jamie Shea, Nato's spokesman, said the alliance has reports of at least two cases at Glogovac and Lipljan in which mass graves had been exhumed, with local villagers being forced to rebury the bodies individually. Diplomats say there is evidence of exhumed bodies being burnt in order to destroy forensic evidence which could assist war crimes investigators. Other corpses have been placed in buildings partially destroyed by bombardments.
At the same time, a US war crimes official said yesterday that at least 5,000 people, and probably many more, had been killed in mass executions in 75 villages in Kosovo. Speaking in Brussels, David Scheffer, the State Department's ambassador-at-large for war crimes, said: "We can only assume the worst and that the figure is actually much higher."
Nato believes the actions by Serb military forces are the result of growing concern about war crimes investigations being undertaken once hostilities in the province have ceased. Mr Shea added: "No matter how much they try to exhume mass graves, the [Hague War Crimes] Tribunal will be on to them in due course."
He poured scorn on reports that President Milosevic had now established a Ministry of Refugees and Humanitarian Issues. He said that, at a time when 90 per cent of the Kosovo Albanian population had been expelled from their homes, it was "the biggest case in history of shutting the stable door after the horse has bolted".
As international concern over atrocities grows, the Foreign Secretary, Robin Cook, announced yesterday that British police will help gather evidence of atrocities in Kosovo. In a Commons debate on the conflict, Mr Cook said a team will work alongside the War Crimes Tribunal investigating sites of suspected massacres.
"They will be forensic experts with experience and expertise in exhuming bodies, gathering evidence about the cause of death and looking for evidence of sexual assault before death.
"We will put their forensic skills and technology to the service of the War Crimes Tribunal in preparing the evidence to bring the perpetrators to justice," he said.
The shadow Foreign Secretary, Michael Howard, welcomed the use of British police officers to assemble evidence of war crimes and said the Opposition continued to support the Government's actions. But he added: "Accounts of atrocities are no substitute for an explanation of the strategy."
The Alliance yesterday also claimed it had new evidence that internal discord over the war was mounting within Yugoslavia, where two recent public gatherings had developed into anti- war rallies. At one incident, in Aleksandrovac, there were scuffles with police after a 1,000-strong crowd gathered to bid farewell to reservists due to return to the Kosovo front.
Mr Shea said the other incident took place at Krusevac, in central Serbia. He said it involved a crowd of 3,000 people protesting about their children being mobilised for fighting and that the event "shows that the spirit of protest is far from lost in Serbia".