Click here for a map showing where the Serbs have closed the border points

Nato and the UN have expressed fears for fleeing Kosovo Albanians turned back from border posts by Serbian troops.

The two main border points between Kosovo and Albania have been closed. And Serbian police have apparently told queues of people, who had been waiting without food on the Kosovo side of the border crossing at Blace in Macedonia, to go home.

BBC Correspondent Paul Wood says refugees in Macedonia have dismissed this as a cynical ploy by Yugoslav President Slobodan Milosevic to demonstrate some kind of normality in Kosovo.

The BBC's Jonathan Charles: "The suffering of the refugees looks set to continue"

European Union interior ministers have been meeting to try to find ways of dealing with the flood of refugees.

But diplomats at the Luxembourg meeting say serious differences are emerging over potential solutions.

France is said to be strongly opposed to a formal airlift, saying it would contribute to ethnic cleansing in Kosovo. Other countries, including Britain and Italy, object to plans for each EU country to be allocated a quota of refugees.

UNHCR worried

Our correspondent says it has always been Yugoslavia's official position that Kosovo Albanians had full rights to remain in their homes. Now the authorities seem to be acting to show they mean what they say.

Jonathan Charles reports: "No doubt that the border is now sealed"

A spokesman for the UN refugee agency (UNHCR), Jacques Franquin, said: "I am very worried. If someone wants to flee his country because he feels persecuted, he should have the right to do that.

"We would like to know what is happening to these people."

Nato alarm

Nato spokesman Jamie Shea said the alliance was alarmed by the border closures.

"It is one thing to push refugees over borders where the international community is increasingly ready to deal with them in a humane way.

"It is quite another to push them back into a wasteland where there is no food, very little water, very little medical supplies and where everything has been looted."

He also said Nato suspected there are three mass graves in Kosovo, and estimated that 50 villages in the province had been torched in the past four days.

Mr Shea said Nato had put five demands to President Slobodan Milosevic and if he agreed to all of them the alliance would stop its air operations.

Signs of genocide

Morina border: now devoid of tractors, cars and people

The BBC's Richard Myron says a sole refugee crossed the Albanian-Serbian border at Morina on Wednesday. The refugee reported that vehicles with people fleeing towards Albania were empty. It was unclear where these people had gone to.

UN Secretary-General Kofi Annan said he saw signs that Serbian authorities were committing genocide in Kosovo.

Ben Brown reports: "100's of buses moved thousands of people"

The US State Department spokesman, James Rubin, has named Yugoslav commanders whose forces were believed to be conducting war crimes or crimes against humanity.

Mr Rubin said he was naming the officers "as a warning that the world is watching".

And US Defence Secretary William Cohen has said Nato will intensify attacks on Serb army units in Kosovo in the coming days.

'Missing' refugees in Albania

Almost 300,000 refugees have crossed into Albania since the conflict began, placing considerable strain on local resources and aid agencies.

Heaps of rubbish left at the encampment

Earlier, the UNHCR expressed concern for the safety of refugees moved from a makeshift camp at Blace, on the Macedonia-Kosovo border, by Macedonian riot police.

Up to 20,000 refugees who apparently vanished overnight have now been traced to southern Albania.

Meanwhile, Yugoslav President Slobodan Milosevic has reportedly offered to hand back three American soldiers through Cyprus as a gesture of goodwill.

The speaker of the Cypriot parliament, Spyros Kyprianou, said he will travel to Belgrade on Thursday in an effort to secure the release of soldiers captured by Yugoslav forces last week.

William Horsley: "The air campaign will continue"

Mr Kyprianou said he had been in negotiations with President Milosevic, who was ready to hand over the soldiers as long as certain conditions were met.

But Nato has said the soldiers' release must be unconditional.

The UNHCR says the number of people who had fled Kosovo since 24 March, when Nato began bombing Yugoslavia, is now more than 600,000.