The UN refugee agency, the UNHCR, said that about 800 people from one train had arrived in the former Yugoslav republic.

The train was stopped and turned back by Serb forces without explanation on Monday after it had reached Djeneral Jankovic, the last station on the Yugoslav side of the border

UNHCR spokeswoman Astrid Van Genderen Stort said most of the refugees came from Urosevac, 45km (30 miles) from the border.

"Most of them are in quite a good state, but the food situation there is very bad," she said.

Refugees had told her the town was full of troops, and Serb soldiers appeared to be trying to stay as close to the population as possible, she said. Some refugees spoke of seeing tanks in and around hospitals and schools, and weapons mounted on ambulances.

Jim Fish reports: "Some of the refugees have been trying to escape for weeks"

However it remained unclear as to why the Serbs had turned the train back.

Ms Van Genderen Stort said: "The Serbs told them the Macedonian border is closed, and that there are Americans over here who won't let them through - all kinds of weird stories."

On arriving in Macedonia, the refugees were loaded onto buses to be taken to a camp further inside the country.

Food running out

The BBC's Jim Fish, who is on the Macedonian border, said some of the refugees, from the Drenica region of central Kosovo, said they had been on the run from Serb police and paramilitary forces since last year.

The Macedonian Government is concerned at the heavy influx of refugees

They reportedly told aid workers they had been beaten by Serb police when they finally reached the border on Tuesday.

World Food Programme officials say they expect many more people to try and escape as food reserves run out and civilians are prevented from buying food in the shops.

One official from a humanitarian organisation suggested that people were being squeezed into ever tighter concentrations particularly around the town of Urosevac, north of the Macedonian border, either as a buffer against Nato attacks or simply to create confusion, our correspondent says.

About 226,500 Kosovo refugees are estimated to be in Macedonia, while several thousand others have been flown out to other host countries.