There is no independent confirmation of the Serb reports, which came after Nato said it had conducted its heaviest day and night of bombing in the air campaign against Yugoslavia so far.

In all, 679 missions were launched in 24 hours, concentrated on Serb forces on the ground in Kosovo, the alliance says.

BBC Defence Correspondent Mark Laity reports with the latest pictures from Kosovo

Chinese President Jiang Zemin has spoken to US President Bill Clinton for the first time since the bombing of the Chinese embassy in Belgrade by Nato a week ago.

And despite threats to abandon mediating efforts, Russia says its Balkan envoy Viktor Chernomydin will make another trip to Belgrade next week, accompanied by Finnish President Martti Ahtisaari.

Heavy strikes

Nato said there were particularly heavy strikes early on Thursday around Prizren, and during the night in the Stimlje area.

The BBC's Peter Grant reports on the latest attacks

The Serb-run Media Centre in Pristina said Nato dropped eight cluster bombs on the village of Korisa at midnight local time (2200 GMT).

The Yugoslav news agency Tanjug said at least 100 civilians were killed in the attack and over 50 injured. Reports said the casualties were mainly women and children refugees.

Nato spokesman Jamie Shea said there was no information yet, but he promised a "full and thorough investigation".

The Yugoslav Ministry of Security Forces says it is halting Sunday's troop withdrawal from Kosovo because Nato has rejected the "gesture for peace" which Belgrade had made.

Yugoslav forces would now remain in Kosovo until Nato troops were withdrawn from neighbouring countries, the statement said.

Nato officials had denied that there had been any significant withdrawal of Yugoslav troops from Kosovo and dismissed Serbia's justification for the withdrawal that the Kosovo Liberation Army had been defeated.

(Click here to see a map of last night's Nato strikes)

US and Chinese presidents speak

China has started to repair the damage to relations caused by Nato's bombing of the Chinese embassy in Belgrade a week ago.

Duncan Hewitt in Beijing: "Clinton's condolence may go some way to appease Chinese anger"

The White House announced President Clinton has spoken on the phone to his Chinese counterpart, Jiang Zemin for 30 minutes.

Spokesman Joe Lockhart said Mr Clinton conveyed his sincere regrets and condolences for the three Chinese nationals who died in the attack, which Nato said was a mistake.

Earlier in the week, the Chinese president had refused to take a call from President Clinton.

Russian mediations to continue

BBC Diplomatic Correspondent Nicholas Witchell: "Nato insists air attacks will continue"

Russian Balkan envoy Viktor Chernomyrdin will visit Belgrade next week for talks with President Milosevic, despite recent Russian threats to abandon mediation efforts.

Reports in Moscow say Mr Chernomyrdin will be accompanied by the Finnish president, Martti Ahtisaari, who is acting as an envoy for the Western powers.

Speculation increased that Mr Ahtisaari was preparing to take a leading role in seeking a solution in the Kosovo crisis when his office announced he would be meetin UN Secretary-General Kofi Annan on Friday.

The two envoys will meet US Deputy Secretary of State Strobe Talbott to co-ordinate their views before they leave for Yugoslavia, Itar-Tass reported.

The UK says said the West will be putting new plans to Russia, said to include a major role for the United Nations.

Mrs Clinton in Skopje

US First Lady Hillary Clinton arrived in the Macedonian capital on Friday to see for herself the plight of more than 200,000 refugees who have fled Kosovo or been driven out since the conflict began.

Mrs Clinton at Stenkovec camp "to show refugees they are not abandoned"

During her one-day visit she is to see Stenkovec camp, which houses some 23,000 refugees from Kosovo.

The Macedonian camps have been the scene of tension and unrest as refugees complain of overcrowding and mistreatment by local police.

President Clinton had said his wife's mission is "to clarify our compassion and concern for the predominantly Muslim Kosovar Albanians who've been driven out of their homes."

UN mission planned

The United Nations is planning to send a humanitarian mission to Yugoslavia on Saturday, for the first time since the airstrikes began.

The 15 UN representatives are to be escorted by Yugoslav police for a planned 12-day exploratory tour of the country including Kosovo.

The mission's leader, the Undersecretary-General for Humanitarian Affairs, Sergio Vieira de Mello, said they had been assured of unhindered access.

The mission follows UN Human Rights Commissioner Mary Robinson's problematic trip to Belgrade where she was refused an audience with President Slobodan Milosevic.

She was highly critical of what she called a Yugoslav government campaign of "ethnic cleansing" in Kosovo, but she balanced it by saying the Nato strikes had brought cruel suffering to innocent civilians in Yugoslavia.

• Refugees recount fresh atrocities
• First Lady visits refugees
• Analysis: Sacking could boost Kosovo peace
• Bulgaria says Nato bombing will succeed
• Macedonia complains over Nato aid

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