The Prime Minister said a second Armoured Battle Group would be sent to support military personnel already in Greece and Macedonia, swelling their number by about 1,800 to 6,300.
"They are being sent so that the UK can be in a position to play our proper role in the international effort, to ensure the refugees are able to return to Kosovo in safety," he said.
"The conflict we now face in Kosovo is a test of our commitment and our resolve to ensure that the 21st century does not begin with a continuing reminder in Europe of the worst aspects of the century now drawing to a close."
The first units will sail today from Emden in north Germany to Thessaloniki in Greece, with the "heavy metal" armoured vehicles leaving on Friday. The troops will fly out to join their equipment when it arrives in about 10 days.
The United States is also preparing to announce greatly increased military involvement in the Balkan conflict.
Washington said it was planning to double the number of its warplanes in the region and was even broaching the call-up of reservists in response to an urgent request from the Nato Supreme Commander, General Wesley Clark, for more airpower. Pentagon sources said the US was on the verge of approving the dispatch of another 300 planes, bringing its total deployed in the region to almost 800, about 80 per cent of the total. The Pentagon said it would ask Congress to authorise up to $4bn in emergency funds to pay for the military operation in Kosovo.
The aircraft would include F-15s and F-16s, more heavy bombers, and air- defence support aircraft, including the EA-6 Prowler, which can jam enemy radar.
More refuelling tankers were also on the list. The Pentagon said: "The goal is to increase Nato's ability to attack Yugoslav army and security forces in Kosovo."
The massive increase in US and British firepower presages round-the- clock bombing raids by Nato, in an all-out attempt to force President Milosevic into submission, but without risking Nato troops in combat on the ground.
In meetings with Congressmen yesterday, the US President, Bill Clinton, was said still to be resisting calls for the deployment of combat troops on the ground in Kosovo.
The escalation of the allied war effort is intended to counter Serbia's continuing systematic deportation of Kosovo's remaining Albanian population.
Yesterday, days after the now forgotten "ceasefire" proclaimed by Belgrade, about 4,000 ethnic Albanians, almost all travelling in tractors and trailers, crossed into northern Albania after being violently forced from their homes by the Serb police.
After crossing the frontier between midnight and dawn yesterday they were directed to fields on the edge of the northern border town of Kukes. Looking confused and dishevelled, they had reportedly been living in the mountains of Kosovo and some had apparently not eaten proper food for almost two weeks.
Some of the refugees said they had witnessed the shooting of a young refugee woman who had resisted being singled out from the rest of her family by the Serbs and taken away for what she feared would be rape.
The Foreign Secretary, Robin Cook, said in London that he believed Albanian refugee women were being forced to endure "systematic rape" at a Serb army camp in Djakovica, near the Albanian border after refugees arriving in Albania told of sex attacks by soldiers.
Mr Cook said the news of the camp had emerged from refugees who had made it across the border. "A number of aid workers have heard the same story from a number of women," he said.
Comparing the Kosovo refugees' experience with the suffering of minorities at the hands of the Nazis in the Second World War, he said: "Nato was born in the aftermath of the defeat of fascism and genocide in Europe. Nato will not now allow this century to end with a triumph of fascism and genocide."Reuse content