"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.
Mr Cook addressed critics of the Nato campaign when he warned that "ending the bombing now would not give an opportunity for diplomacy, but would knock away the best lever of diplomacy".
He said: "It would enable Milosevic to regroup, rebuild and re-equip his forces and that would prolong, not end the conflict on the ground ... but most of all we cannot abandon the bombing without abandoning the refugees themselves."
But Edward Leigh, the Tory MP for Gainsborough, intervened to challenge him on whether "bombing alone could do the trick".
The Foreign Secretary indicated that Nato's secretary-general, Javier Solana, was expected to give a new figure tomorrow for the number of ground troops needed to enforce a ceasefire during the reconstruction of Kosovo. Foreign Office sources said later that the number estimated at Rambouillet was 28,000, but that about 40,000 troops were now likely to be needed.
Mr Cook added: "We are determined that the Kosovo crisis must be made a turning-point for the region. But there will be no stability or a fresh start for the Balkans if we do not defeat the ethnic cleansing of Milosevic that belongs to the fascism of yesterday and not the Europe of today."
The shadow Foreign Secretary, Michael Howard, stressed his party's support for the military action but defended his right to scrutinise Nato's strategy. "Accounts of atrocities are no substitute for an explanation of the strategy," he said. It was "no good" the Government repeating Nato's objectives and accounts of the atrocities in Kosovo "if we are not making sufficient progress in achieving the objectives".
He went on: "It is no use pretending, in the eighth week of this action, that the objectives have been achieved or that we are close to achieving them, when all the indications are that that is not being done."
The Government had shown "a steady change" in its position on ground troops. "We have supported your objectives. We have supported your decision to take action.
"We are not in a position to support you on these various changes of position, because they have never been properly or convincingly explained," Mr Howard said.