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Nato has launched a Cruise missile attack on Belgrade from ships in the Adriatic for the second night running.

Reports from the city spoke of a series of explosions and an orange glow lighting up the sky.

Serbian television said a fuel storage facility and an industrial plant had been hit. Yugoslav officials said a police academy on the outskirts of the city had also been struck.

The all-clear siren sounded at 0709 local time (0509 GMT).

John Simpson in Belgrade: "The extent of the damage is clear by daylight"

The latest strikes followed Nato's announcement that it was setting up a humanitarian operation in Albania with more than 6,000 troops to cope with the deepening refugee crisis.

Eyewitnesses on board one of the American warships in the Adriatic said several Cruise missiles had been launched. War planes were seen taking off from the Aviano airbase in northern Italy.

Meanwhile, the US has announced it is sending an aircraft carrier, the USS Theodore Roosevelt, to the Adriatic to join the Nato operation. The Pentagon said it should arrive in the region on Monday.

Serb TV showed footage of the bridge under attack

On Saturday night, Serb state-run TV said Nato jets attacked a key bridge over the River Danube in northern Serbia.

It said there was civilian traffic on the bridge in the city of Novi Sad when the bombs fell. The reports said seven civilians had been injured in the attack.

A second bridge over the Danube near the Croatian border was also hit, TV reports said.

Last Wednesday, alliance forces destroyed another bridge in Novi Sad.

BBC correspondent in Belgrade Michael Williams says the air strikes are uniting the Serbian population behind President Milosevic's leadership - every day there are popular demonstrations in Belgrade and other towns and cities across the country.

Video 'shows Serb massacre'

Meanwhile, the BBC has broadcast video pictures which appear to confirm eyewitness accounts of Serb atrocities in Kosovo.

The young men were reportedly shot one by one

The tape, made by an ethnic Albanian who smuggled it out of the province, shows a number of bodies of men lying in pools of blood in streets and fields. Many have bullet wounds to the back of the head or under the jaw.

The film-maker, Milaim Bellanica, said he went into hiding and made the film after the Serbs left. He then risked his life to smuggle it to Macedonia.

No ground troops

The US has repeated that Nato does not not plan to use ground forces to invade Kosovo, despite the escalating humanitarian crisis.

Pentagon spokesman Ken Bacon said: "There is not an intentional plan to put a ground force into a combat environment, to invade Kosovo."

Battles for food: Supplies are scarce

The announcement came as refugees continued to pour out of the province. Border officials say more than 20,000 have crossed into northern Albania in the past 24 hours.

The UN refugee agency said on Saturday that about 315,000 Kosovo Albanians have fled or been expelled since the air strikes began. Nato says at this rate the Serbs will empty their southern province within another 20 days.

Nato is setting up a headquarters in Albania to co-ordinate the humanitarian effort, while Macedonia has closed its border claiming the massive influx is threatening an economic and social crisis.

It says it will only allow entry to those who have guaranteed passage to other countries

Ben Brown on the Kosovo-Macedonia border: "Disease is spreading and people are dying"

An estimated 50,000 refugees are stuck at the Blace border post in freezing temperatures. Disease is said to be spreading and 11 people have died since Friday.

Some refugees have threatened to march out of the camp into Macedonia.

Security forces are standing by in riot gear with automatic weapons to prevent any unauthorised move from the border area.

Mr Cook has proposed creating official sanctuaries within the country to deal with the crisis. "The proposal has been greeted with interest by the Macedonian Government," he said.

Nato chief hardens war aims

Meanwhile, Nato Secretary General Javier Solana has toughened demands for Kosovo, telling Yugoslav President Slobodan Milosevic to pull all forces out and accept a Nato-led force to escort ethnic Albanians home.

Hannu Pekka Laiho of the Red Cross: "People are really suffering"

Previously Nato had committed itself to the terms of the Rambouillet agreement, under which the Serbs would only begin withdrawing troops after a peace deal which would still allow a small force to remain.

The shift in strategy has not yet been endorsed by the alliance as official policy.

The Rambouillet peace deal was agreed by the Kosovo Albanians but not by Mr Milosevic who has always opposed the presence of foreign troops in the province.

The latest air strikes come less than 24 hours after Nato escalated its bombing campaign in Yugoslavia, hitting the heart of the capital Belgrade for the first time.

Two ministries described by Nato as the "brain" of the Serb ethnic cleansing operation in Kosovo were destroyed by Cruise missiles.