His visit to the former Yugoslav republic is intended to reassure the government of the UN's continuing help in easing the refugee burden there.

The UN has been able to fly more refugees out to third countries than have been coming in from Kosovo, but over the last three days aid agencies have reported a renewed surge in numbers.

Several hundred more crossed into Macedonia during Mr Annan's visit to the border post. UN officials say that the latest arrivals have told them that another exodus of 20-30,000 refugees was headed for the border.

The BBC's Jim Fish reports: Mr Annan's visit has done little to restore confidence in the UN

Earlier the human rights group Amnesty International criticised the Macedonian authorities for their handling of the refugees.

It said the Macedonian police were intimidating refugees in the camps and said Macedonia's frequent closure of its border meant would-be refugees were being sent back to face great danger and possibly death.

Border assurances

But Mr Annan said the Macedonian prime minister had assured him the border would stay open.

Macedonian officials have repeatedly expressed concern that the large number of refugees entering the country could upset the country's fragile ethnic balance.

(Click here to see a map of the most recent refugee movements)

Macedonian police have been criticised for their treatment of refugees

On a visit to the main refugee camp at Brazda, the secretary-general was cheered by hundreds of Kosovo Albanians as he toured the rows of tents.

However Mr Annan's tour quickly descended into chaos as his entourage was overwhelmed by the media, preventing him from speaking to the refugees.

The short press conference he was able to give did not offer much hope for their early return to Kosovo.

No promises

"Preferably (the refugees) will not spend the winter here," Mr Annan said. "But I cannot give you that assurance."

Mr Annan says the UN must play a role in a future peace plan

The secretary-general, who is due to travel on to Albania on Thursday, said he believed that the UN would have to play a central role in any peace accord on Kosovo.

He said it was "important that the international community, under the umbrella of the UN, pool its efforts and collectively sort this situation out."

So far the UN has been kept on the sidelines of diplomatic efforts to end the crisis after Nato went ahead with its air campaign against Yugoslavia without a mandate from the Security Council.

Refugee Website

In an attempt to help reunite refugee families separated by the crisis, the International Committee of the Red Cross has launched an Internet site on which refugees will be able to search for missing relatives or enter their own details.

The Red Cross says it hopes that by using the Internet, relatives will be reunited more quickly than would otherwise be possible.