Nato spokesman Jamie Shea said Serb forces in Kosovo had organised "grave digging chain gangs", making the men wear red so they could be easily identified.

Nato also says men and boys in Kosovo are being forced to dig coal around the capital Pristina to maintain electricity supplies.

Earlier on Sunday, the UK's Armed Forces Minister, Doug Henderson, said Kosovo Albanians were being forced to clear bodies from towns and villages ransacked by Serb forces.

He also told a Ministry of Defence briefing that more than 20,000 refugees had fled Kosovo during the previous 24 hours. He said it was estimated that another 20,000 were at the borders intending to cross.

The BBC's Kevin Connelly: "Further reminders of the moral justification"

Nato has evidence of the Serbs destroying 200 villages and towns, and "disturbing reports" of prisoners being used to try to cover up evidence of massacres, he told the briefing in London.

He said British troops were "ready to extend" their work in building camps and help the international aid mission.

Refugees crossing from the Kosovo border into Albania

The UK's Deputy Chief of Defence said that in spite of the mixed weather during the past 24 hours, Nato had attacked targets in Serbia and Kosovo.

Air Marshal Sir John Day said RAF harrier GR7 aircraft hit Serbian army and special police forces in Kosovo with RBL755 cluster bombs.

"We do not yet have the full battle damage assessment, but initial reports say they hit both armoured personnel carriers and military soft-skin vehicles," he said.

Saturday's attack also targeted airfields and oil depots, he said.

This showed that Nato was "making inroads" into Serb President Slobodan Milosevic's forces in Kosovo, which were "directly responsible for the ethnic cleansing".

There are 40,000 Serb army personnel and 300 tanks in Kosovo, and cutting their lines of communication will make them more vulnerable to attack, Sir John added.