The Pentagon has acknowledged that Nato pilots bombed a column of military vehicles which had been near civilian vehicles on Wednesday.

In a separate incident, Yugoslav aircraft were reported to have attacked another refugee convoy.

Despite the casualties, Nato raids continued across Yugoslavia on Thursday morning, with five or six powerful explosions shaking the capital, Belgrade.

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A Serbian official said army barracks at Racovica about 8km from the city centre had been hit, and power supplies to the region cut.

Serbian media said Nato bombs had destroyed a bridge in Krusevac, about 100km south of Belgrade, linking the town to the Kosovo capital of Pristina.

Earlier, the Yugoslav news agency, Tanjug, said a television transmitter southwest of Belgrade had been struck by a Nato missile.

An eyewitnesses describes the attack

In another report, Tanjug said Nato warplanes had attacked the town of Kragujevac in central Serbia, hitting the town centre.

The attacks came as the Pentagon tried to clear up Serb allegations that Nato had killed refugees travelling on the Prizren-Djakovica road in west Kosovo.

A spokesman said Nato aircraft had engaged military vehicles near Djakovica and had broken off when the pilots saw civilian vehicles, but not before bombs had been dropped.

Serb media said 64 people had been killed and 20 wounded in the Nato attack. State television has released pictures of the dead and wounded.

The Pentagon withdrew earlier allegations that Serbs troops had attacked a civilian convoy after military targets were hit.

A Pentagon official told the BBC: "We do not know whether the convoy was military, civilian or a combination of the two."

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BBC Washington Correspondent Paul Reynolds says it appears that Nato aircraft might well have been responsible for the casualties.

In a separate incident on Wednesday, Yugoslav aircraft had attacked a column of civilians between Prizren and Kukes, in Albania, refugees reaching Albania said. Two tractors were said to have been destroyed.

Albania's opposition Democratic Party said refugees arriving from Kosovo had reported that Serbian helicopters had attacked them on Wednesday, killing at least 40 people and wounding many others.

BBC Correspondent Duncan Kennedy spoke to the refugees

Refugees crossing into Northern Albania on Wednesday night told the BBC that they had seen 15-20 bodies after their convoy had come under air attack.

They said they were being forced out of Kosovo into Albania when they were attacked.

They said that after hearing at least one explosion they saw Serb police and military units in the area.

The incidents came two days after a Nato aircraft hit a passenger train in an attempt to destroy a bridge in southern Serbia - 27 people are reported to have died in that attack.

(Click here for map of latest strikes)

Intensive talks

The attack comes on top of the refugees' many other problems

The reports of the air strikes came as EU leaders and United Nations Secretary-General Kofi Annan met to try to find a solution to the three-week conflict.

Within Kosovo, the United Nations food agency has warned that refugees trapped in the province are facing a severe and long-term food shortage.

It said Kosovo's agricultural and food-processing industries have been devastated, with most fields abandoned and huge numbers of livestock dead.

Latest UN figures say 536,000 people have fled Kosovo - half of them to Albania.

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