Mr Cook, representing the Contact Group of five Western powers and Russia, is warning the two sides that Nato is ready to go ahead with air strikes if they ignore demands to negotiate.

James Robbins reports: Robin Cook's message was: "No one can win this war"

While Mr Cook delivered his message in Belgrade, Nato officials were meeting in Brussels to put the final touches to a military plan should his mission fail.

The Contact Group, backed by the United Nations, has given Belgrade authorities and ethnic Albanian leaders in Kosovo three weeks to negotiate an agreement on "substantial autonomy" for the troubled province or face military action.

Under the plan, both sides will have to meet within a week.

But the situation on the ground in Kosovo remains tense with the discovery of the bodies of 24 ethnic Albanian men in the western village of Rogovo on Friday.

The dead, who included three men wearing Kosovo Liberation Army (KLA) uniforms, were apparently killed by Serbian security forces following an ambush in which a Serb policeman was killed.

Later a bomb exploded near a cafe frequented by Serbs in the capital, Pristina, injuring seven people. The police said they found a message at the scene saying the bomb was to avenge KLA deaths.

International warning

Paul Wood reports: Mr Cook came away without a definitive answer from Serbia

Mr Cook had a 30-minute meeting with Yugoslav President Slobodan Milosevic in Belgrade, before flying on to meet ethnic Albanian leaders to impress upon them the need for agreement.

Mr Cook received no definitive answer from the Yugoslav president over the international proposals, but after the meeting he said Mr Milosevic had agreed to study the plans and would respond within a few days.

"President Milosevic has assured me that he is committed to a peaceful solution," the UK foreign secretary said.

British officials said the threat of Nato military force was explicitly put to the Yugoslav president, although there was no discussion of the possible need for ground troops to enforce a settlement, according to the BBC's correspondent.

However Mr Milosevic indicated continued resistance to the Contact Group's demand that the peace talks be held in France.

The official Tanjug news agency said: "President Milosevic said it was well known that Serbia and Yugoslavia were firmly committed to resolving problems in Kosovo, which is an integral part of Serbia, peacefully in Serbia with the participation of the representatives of all ethnic communities."

European back-up

Mr Cook's scheduled meeting with moderate Kosovo Albanian leader Ibrahim Rugova and Adem Demaci, the political representative of the KLA, was moved from Pristina to the Macedonian capital of Skopje because of heavy snow.

Correspondents said he would be telling ethnic Albanian leaders that Kosovo can expect European ground troops to back up any promise of autonomy from Serbia if the KLA co-operates, according to our correspondent.

If the KLA turns its back on this chance for substantial autonomy, it risks facing increasing international isolation, according to correspondents.

Both Belgrade and the moderate ethnic Albanian leadership have welcomed the idea of talks and say they will send representatives.

But leaders of the independence-seeking ethnic Albanian majority in Kosovo, including the KLA, said Belgrade would have to implement a ceasefire first and withdraw its forces from the province.