Raising the temperature on the Belgrade regime, Mr Cook yesterday underscored the message that international law against genocide will be used to prosecute those apprehended.
The Ministry of Defence published names of those held accountable for the war crimes, starting with Slobodan Milosevic, with their position in the Serbian hierarchy.
The list also includes Lieutenant-General Radomar Markovic, the head of state security; Lieutenant-Colonel-General Pavokovic, formerly in charge of Kosovo operations and who is related by marriage to Mr Milosevic; Colonel- General Dragolub Ojdanic, one of the leading hardliners, and Major-General Lazervic, involved in directing the campaign against the Kosovo Liberation Army.
The Ministry of Defence also issued a list of 17 villages destroyed by Serbian forces since the campaign started in February l998, with the number of inhabitants killed.
As Nato warplanes continued to pound Yugoslav defences and to target troops on the ground, another kind of offensive is also going on - to foment a revolt in the Yugoslav high command, it was disclosed yesterday.
George Robertson, the Secretary of State for Defence, visiting RAF pilots at the Gioia del Colle airbase in southern Italy, said that efforts were being made to turn military commanders away from the Milosevic regime and its "ethnic-cleansing" policy in the hope that they would stop the slaughter.
"He can't conduct `ethnic cleansing' on this scale without troops and without commanders right down the line," said Mr Robertson.
"Some of these people are proud soldiers who are not used to killing old women and young children."
Dismissing the Yugoslav Interior Ministry Police as "uniformed thugs", he said that many of the atrocities carried out over the past few days had been actions taken by individual commanders.
By contrast, he said, there were commanders in the Yugoslav Army who had grown up in the military and who had decent standards of behaviour.
He quoted the example of Momcilo Perisic, who was dismissed as Mr Milosevic's army chief for criticising the President over his policy of confrontation with Nato.
"There are decent people inside that structure who do want to hold on to Kosovo but who do not want to go down in history as successors to the Nazis. They are the group of people that message has to get through to," he said.
"I don't believe for a minute that there is unity of purpose within the whole regime."
Targeting these people was the reason for repeated statements on television that atrocities were being recorded and those responsible would be referred to the International War Crimes Tribunal in The Hague. "We are saying to them `we are watching, we know what you are doing, we know who is doing it, and that information is going to The Hague'," said Mr Robertson.
The Secretary of State for Defence, who also addressed ground crew at Gioia del Colle, said the tempo of operations would increase.
But he gave a warning that the danger to pilots would also intensify.
"Risks are very high, of course. They are obviously increasing all the time. But these are very brave people," said Mr Robertson. "This is not going to be quick and it's not going to be easy."
Operation Allied Force moved to Phase II over the weekend, allowing the direct targeting of Serb ground troops in Kosovo.
Mr Robertson admitted this had been done earlier than planned because of the unfolding humanitarian crisis. He also conceded that the Nato attacks may have made the situation worse. "But if it has made it worse, it has made it worse for a temporary period before it gets better."
Deploying ground troops effectively to invade Yugoslavia "was not a sensible option", he said. To assemble the number of troops required would take about two months, "assuming you could find enough troops that are fit and ready to go into battle".
The British Army already has 4,800 troops in Macedonia and a total of 8,500 ready to be deployed on a peacekeeping mission in Kosovo. This brings the total of British soldiers either preparing for operations, on operations or recently returned from operations to 41 per cent of the total. This, said Mr Robertson, was the highest figure ever in peace time. Kosovo would also be the most inhospitable fighting territory imaginable.
In a show of political unity, Mr Robertson was accompanied on the visit by Menzies Campbell and John Maples, the Liberal Democrat and Conservative defence spokesmen.