The raids were to stop President Milosevic carrying out "the vile oppression" of Kosovo Albanians, he said.

"There are times when we have to stand up and fight for peace," he said at 1915 GMT, shortly after cruise missiles struck targets in the region.

UK Harrier jets were involved in the first wave of air attacks.

Tony Blair: "If there is retaliation, our response will be swift and severe"

Mr Blair said that Kosovo was on Europe's doorstep, and events there would be felt throughout Europe.

"Any political leader thinks long and hard before committing forces to action . . . I would not do it if I did not think it was the right thing to do," he said.

George Robertson: Only military targets would be attacked

Nato warplanes took off from their bases in Italy shortly after 1800 GMT. About an hour later loud explosions were heard around Kosovo's regional capital, Pristina.

All eight B-52s have now returned to RAF Fairford, in Gloucestershire, six of them were involved in air attacks over Yugoslavia.

In a Commons statement Deputy Prime Minister John Prescott told MPs four British aircraft together with the submarine HMS Splendid had attacked targets in the federal republic of Yugoslavia.

John Prescott: "What happens next is up to Milosevic"

They were acting as part of the Nato task force, he said.

Mr Prescott then paid tribute to British servicemen, servicewomen and their families.

"Tonight there will be families in Britain who will be feeling a real sense of anxiety.

"They can too feel a real sense of pride in the contribution their loved ones are making to peace and stability in Europe," he said.

The deputy prime minister told the House the first Nato targets had been air defence systems and "facilities relating to the suppression in Kosovo".

Mr Prescott warned MPs there would be "no instant end" to the suffering in Kosovo. He said the air strikes would continue until military objectives were met.

What happened next, Mr Prescott said, would be up to President Milosevic.

Defence Minister George Robertson: Averting humanitarian disaster is justified aim

Earlier, Defence Secretary George Robertson expressed confidence that Nato ground forces in Macedonia and Bosnia could defend themselves if they were attacked by Yugoslavia.

He said the Nato troops were on peace-keeping duties and any attack upon them would be "a gross violation of international law" and would result in "an immediate and considerable response from us".

But he reiterated that ground forces would not cross the border into Kosovo until there was a political settlement in place for them to police.

'Courage and professionalism'

Leader of the Opposition William Hague backed the raids, saying: "A threat once made must be backed up and that is what is happening tonight and so the opposition support the government in doing that."

William Hague: Thoughts are with UK forces

Although he said the Conservatives had concerns about the future of the operation and the possible involvement of British troops in a ground war in the Balkans, he supported the use of UK armed forces in the conflict.

He said: "Our forces are going into action with great courage and professionalism where they have got to do that which has to be done.

"Tonight we should, across politics, be backing them up and wishing them well."

'Clear objectives'

Speaking earlier in the House of Commons, Liberal Democrat leader Paddy Ashdown said the air strikes must have "a clear, definable and achievable political aim which indicates what we are trying to achieve and tells us when we should stop".

He added that if President Milosevic could not be made to sign the peace agreement the air raids should be "seen as a first step towards establishing an international protectorate in Kosovo".

Some Labour MPs attacked the decision to order air strikes, claiming Nato's action had not been endorsed by the UN Security Council or the six-nation Contact Group on Kosovo.

In a Commons early day motion, six left-wing backbenchers - veteran MP Tony Benn among them - said the move "contravenes the sovereign status of a recognised state, is likely to cause further civilian casualties and could lead to an escalation of conflict with consequent increased loss of life on all sides".