The Foreign Secretary, Robin Cook, said yesterday that he believed almost 400,000 people inside Kosovo were in hiding, cold and starving, in the mountains. His account was based on a telephone conversation with Hashim Thaqi, one of the leaders of the Kosovo Liberation Army (KLA).
Mr Thaqi has his own agenda, which is to deepen the West's involvement. And with 1.5 million people on the move, out of Kosovo's population of 1.8 million, it is difficult for observers to monitor the ethnic cleansing carried out by Slobodan Milosevic's forces.
But Kosovo refugees now in Albania and Macedonia have consistently spoken of men being rounded up and taken away by Serb militiamen.
Mr Cook's concern, shared by Nato, is based on the situation in the refugee camps, where aid workers have noted the fact that adult males make up only 10 per cent of the intake. It means at least 100,000 men are missing, though the figure may be much higher.
Some of these men may have decided to stay in Kosovo to fight in the ranks of the KLA. But there is now widespread apprehension about the fate of the rest. Clare Short, the International Development Secretary, said that President Milosovic's regime will be brought before war crimes tribunals for any crimes committed against the Kosovo Albanians.
Nato's fears have received some confirmation with reports of mass graves. The alliance yesterday released satellite pictures purporting to show what could be the site of a mass grave in the central town of Orahovac.
The alliance said last week that it believed large-scale killings by Serb authorities were taking place. Nato's spokesman, Jamie Shea, said it was up to the International Criminal Tribunal, set up in The Hague, to investigate the matter in the future.
The West's fears are based on experience of the 1992-95 war in Bosnia. In the summer of 1995, after over-running the eastern town of Srebrenica, the Bosnian Serb army separated men from their families and killed as many of them as they could.
The ruthless operation was designed to make sure they never joined the Bosnian government army - as well as demonstrating the Serb obsession with halting the growth of the Muslim population. At the time, most governments in the West regarded the claims of Serb atrocities as propaganda.
Kosovo refugees have given details of where a number of mass graves containing young men are sited. One is near Podujevo, in the north of the province, a former KLA stronghold. More than 200 men are said to have been shot there.
Other sites are at Malakrusa, where there were reports of shootings and burnings. There are said to have been further killings at Pastasel, Velika Krusa, Suva Reka, Kosovo Polje and Malisevo.
The refugees have made other claims that mirror the grim events of the Bosnian conflict, which pitted Serbs, Muslims and Croats against each other. While the men have been taken away, Kosovo women are said to have been raped at checkpoints. Many of the victims have been too ashamed, it is said, to tell aid workers what happened.
There are also allegations that the Serbs have been setting up "rape camps", where their victims have been shot and buried, after being imprisoned and abused. A Pentagon spokesman, Kenneth Bacon, spoke of "an eerie and disturbing echo of instances of rape and killing of women during the Bosnian war".
Unlike at the time of the Bosnian war, the West is now prepared to accept the worst possible reports about the behaviour of Serb forces, even if the numbers mentioned are treated with caution.
There is no intrinsic reason, say observers, why the Serb forces should have changed their ways.
For Nato, the reports are another reminder of the problems of its current strategy. Not only are air strikes failing to stop the abuse of the civilian population, there is a severe lack of knowledge about what exactly is going on in Kosovo.Reuse content