President Clinton said early today that NATO had launched its air strikes "to defuse a powder keg in the heart of Europe".
In a nationally-televised address from the White House, he said the US had a duty to intervene, along with its NATO allies, in the Kosovo crisis.
"Ending this tragedy is a moral imperative. It is also important to America's national interest."
He noted the complex ethnic make-up of the region and said "all the ingredients for a major war are there".
"I am convinced that the dangers of acting are far outweighed by the dangers of not acting" to halt the conflict in Kosovo.
Other key players in the attacks on Yugoslav military installations had moved swiftly last night to justify their actions as regrettable but necessary.
In Brussels Mr Javier Solana, the Secretary-General of NATO, many of whose member-states took part in the raids, said the strikes - the first in the 50-year history of the organisation launched against a sovereign state without an explicit mandate from the United Nations - were caused by the obduracy of Mr Slobodan Milosevic.
"In the last months the international community has spared no efforts to achieve a negotiated solution. But it has not been possible," Mr Solana said. "Clear responsibility for the air strikes lies with President Milosevic, who has refused to stop his violent action in Kosovo and has refused to negotiate in good faith . . . We must stop the violence and bring an end to the humanitarian catastrophe now taking place in Kosovo. We have a moral duty to do so."
The British Prime Minister, Mr Tony Blair, referred to Mr Milosevic as a man who had brought "death and barbarism" to the Balkans. He said: "Kosovo is right on Europe's doorstep. As previous Balkan crises have shown, the effects are felt far and wide. There are more than one million refugees from former Yugoslavia in EU countries . ..
"Britain is a peaceful nation. We are a peaceful people who take no joy in war. But we know from our own history, and from our own character, that there are times when we have to stand up and fight for peace."