The United Nations refugee agency and US State Department say the 10,000 missing refugees are either in Albania or on their way there.

It means Albania has now accepted about 20,000 of 40,000 refugees moved out of Blace border camp by the Macedonian authorities.

Others were moved into Macedonia or transferred to Greece.

(click here for a map of refugee movements)

But fears are growing for other refugees, who have reportedly been forced back into Kosovo by Serb forces as they tried to leave the province.

The UNHCR says most of the Kosovo Albanians who were moved in the middle of the night from Blace have been traced.

And State Department spokesman James Rubin said only a small minority were still unaccounted for.

Families separated

Fergal Keane on the Albanian border: A sense of bewilderment among the refugees

Aid workers are furious over the operation at Blace. They say many families have been split up and may never be reunited.

Others refugees had passports and identity cards taken from them.

Aid agencies say there were enough places for these refugees inside Macedonia in camps just built by Nato troops.

'Human shields'

Concerns are growing that the Serbs may be pushing thousands of refugees back into the province in order to use them as human shields.

Blace was emptied in one night

The Yugoslavs suddenly closed the borders to Albanian and Macedonia on Wednesday after forcing around 450,000 people out of the country in the last weeks.

Thousands of refugees who had been waiting on the frontier were turned back to villages or towns said to have been ravaged amid the campaign of forced expulsions.

"The refugees ... were told to return to their places of residence - whatever is left of those places," said Doran Vienneau of the Organisation for Security and Cooperation in Europe, which has been monitoring the border.

The BBC's David Sillito: Aid workers do not know what has happened to all the refugees

Britain's international aid minister, Clare Short, pointed to a "worrying change in Serbian tactics".

Nato Secretary General Javier Solana said Yugoslav President Slobodan Milosevic could be planning to use refugees as human shields or wanted to avoid pictures of a mass exodus being broadcast round the world.

"He could be trying to use people as human shields in case the alliance's military action is concentrated more on the ground," he added.

Along the Albanian border, Yugoslav guards have been seen laying what appear to be mines and digging fortifications.

The UNHCR says more than 600,000 people, nearly a third of Kosovo's population, have fled the province since Nato began bombing Yugoslavia.