The disclosure came as Serb forces turned back a trainload of up to 2,000 refugees at the Macedonian border in what aid workers said was further evidence of the "psychological warfare" being waged by Serbia against the civilian population of Kosovo. The refugees were forced to head back north inside the province. The sound of explosions heard from across the border afterwards raised fears for their safety.
Refugees who witnessed the train incident said people had packed into the train in southern Kosovo, with mothers pushing little children in through its windows and in some cases failing to get on themselves.
"Why would they stuff refugees onto a train, then refuse to let them off. What other reasonable conclusion can you draw but that this is psychological warfare," said Sandy Blyth of the Organisation for Security and Co-operation in Europe (OSCE), adding that being turned back would have a devastating psychological impact on the refugees.
The Foreign Secretary insisted, meanwhile, that more than 100 civilians killed by Nato bombs at the village of Korisa last week had been taken as human shields. They had been hunted out of their hiding place in woods near the village, rounded up and forced to camp in a military barracks. Nato confirmed on Saturday that it dropped eight bombs on Friday on the compound, a "legitimate" military target.
"The responsibility for that tragedy rests with the Serb forces who... forced those 100 refugees not to return to their homes but to settle, squeezed together, in those two compounds," Mr Cook said.
One survivor of the Korisa bombing told German radio that about 600 people were forced to gather on a small plot of land near Korisa before the attack. "We were told something bad would happen to us if we left the place," he said. He quoted a Serb policeman as saying: "Now you'll see what a Nato attack looks like."
The human shield tactic, if as widely used as Mr Cook claims, indicates wholesale disregard by the Serbs for the laws of war as laid down by the Geneva Conventions. Yugoslavia is a signatory of the 1949 treaty which prohibits attacks or threats of violence against the civilian population caught up in an armed conflict.
There is growing evidence of other blatant Serb violation of the Conventions: the rape of Albanian women, the taking of hostages, and the dumping of corpses into the water supply, for example.
But there are also growing concerns about Nato's violation of the Conventions. The alliance's high-altitude bombing, designed to minimise its own losses, may be illegal, according to the New York-based organisation Human Rights Watch.
Article 51 of Protocol 1 of the Geneva Conventions forbids attack by any method which treats as a single target a number of clearly distinct military targets in a town or village which also contain a similar concentration of civilians.Reuse content