Officials in the Macedonian capital, Skopje, say the country has taken in too many refugees since Nato began its air campaign in March.

They have expressed fears the refugee influx could upset the country's ethnic balance and aggravate economic problems.

Last week, the Macedonians decided to close their border with Kosovo, but the Albanian govenrment said it was willing to take in more people and Nato has agreed to build new camps there.

Closure 'unacceptable'

Macedonia says its camps are already overcrowded

The decision met with criticism from the European Union's Humanitarian Aid Commissioner, Emma Bonino who is due to hold talks with the Macedonian Prime Minister, Ljubco Georgievski, on Sunday.

"Even if I understand their political situation and fragility, this is something that from a humanitarian point of view and the Geneva Convention is simply not acceptable," she told reporters in Albania on Saturday.

The BBC's Clive Myrie in Kukes, Albania: Macedonia says it has its internal security to consider

Ms Bonino said a first group of up to 6,000 refugees would arrive in Albania on Sunday and could number up to 6,000.

She said the ethnic Albanian refugees already driven out of Kosovo by Serb forces were reluctant to move a second time and they could not be forced to do so.

(Click here to see a map of refugee movements to date)

Thousands of refugees are expected to be moved south in coming days

On Saturday, about 6,000 new refugees crossed the border into northern Albania, most of them coming from Kosovo's second city, Pec, in the north-west.

Aid workers say a major offensive on the part of Serbian paramilitaries, police and army, resulted in this latest wave of refugees.

A number of those reaching the border told the BBC the authorities in Kosovo began moving thousands of people on Friday from more than 20 villages near Pec.

Most of the refugees were in cars or in tractor trailors and at one point, it was estimated the tailback of refugees stretched for five kilometres (three miles).

Serb attrocities

The BBC's George Eykyn in south-eastern Albania: Engineers are working flat out to build the new camps

Once again, many brought with them stories of Serb atrocities.

One group of people from the village of Djarakovic said when paramilitaries and the police entered their village, they rounded up about 300 men and took them away.

Others from the village of Nabujan said men were being taken away to be executed.

The BBC's Clive Myrie, in the northern Albanian town of Kukes, says many of those crossing the border were dehydrated and clearly traumatised by their experiences.

Most were quickly transported further south.

The UN refugee agency has said, because of increased Serbian military activity in the border region, they would try to empty all the camps there as quickly as possible.