Nato has launched the first wave of strikes against Serbian military targets, fulfilling weeks of warnings of military action over the Kosovo crisis.

US defence officials said the attacks, the first against a sovereign country in Nato's 50-year history, began with air and sea-launched cruise missiles.

The many threats against President Milosevic were finally acted on with explosions first heard at about 1900 GMT.

Jeremy Cooke in Belgrade sees "a bright orange flare tracking across the sky"

Russia's President Boris Yeltsin has recalled the country's representative at Nato's Brussels headquarters and ordered a halt to all co-operation with the alliance.

The UN's Security Council is due to meet at Russia's request at midnight GMT Wednesday.

BBC Correspondents and news agencies have reported explosions in Serbia and Montenegro including:

• Suspected strikes against the large Batajnica military air base near Belgrade.
• Strikes against an aircraft factory near the capital.
• At least three explosions at Novi Sad, north of Belgrade.
• Hits against the Zastava weapons plant in Kragujevac.

Correspondents in the Kosovo capital Pristina report:

• Large explosions shortly before 1900 GMT.
• A loss of lighting and power in the capital.
• Repeated soundings of air raid sirens.

Jacky Rowland in Pristina at 1925GMT: "It's dark. It's silent. Everyone feels that they have lost control of their lives."

In its first reports, the Yugoslav news agency Tanjug say that some family members of government forces have been killed.

The agency also reported that seven Serbian towns had been hit in the first wave of Nato attacks.

The missile strikes are expected to pave the way for huge bombing raids on Serb forces by up to 400 Nato warplanes on standby in the region.

Nato Secretary-General Javier Solana announced the beginning of the operation after waves of Nato planes took off from the an airbase at Aviano in northeastern Italy at nightfall.

Hours earlier, eight American B-52 bombers, armed with cruise missiles, left from an airbase in England.

Speaking shortly after the announcement of the attacks, President Bill Clinton said the aim of the action was threefold: to demonstrate Nato's opposition to agression, to deter President Slobodan Milosevic from further attacks and to diminish the Serbs' military capability.

''Kosovo's crisis is now full blown,'' he said. ''If we don't act clearly it will get even worse.

"Only firmness now can prevent greater catastrophe later.''

Military observers say the warplanes will meet a stiffer challenge than air missions over Iraq; western leaders have acknowledged they risk casualties.

Yugoslavia was placed on high alert after the government declared a state of emergency. Military preparations included setting up air-raid shelters and bunkers for civilians.

Thousands of Kosovo Albanians have been fleeing the latest Serb-led offensive, heading south into the former Yugoslav republic of Macedonia.

Defiant Serbs

On Wednesday afternoon, Serb leader Slobodan Milosevic called on his people to be prepared to defend their country "by all means".

In a nationally televised address he warned them that "at stake is the freedom of the entire country".

"We shall defend the country if it is attacked," he said.

But blaming Yugoslav Government "intransigence", the Nato secretary-general has said Nato's quarrel was not with the Yugoslav people and that the attacks would be aimed at weakening the Yugoslav army and paramilitary police forces.

'New Vietnam warning'

President Boris Yeltsin appealed to world leaders in a national television address on Wednesday to keep Bill Clinton from making what he described as a "terrifying and tragic" mistake of launching air strikes against Serbia.

Its Prime Minister, Yevgeny Primakov has warned that Russia's relations with Washington will be damaged and European stability harmed.