After seeing both the Serbian President Milan Milutinovic and the ethnic Albanian delegation, Mr Cook strongly criticised the Serbs' tactics in the negotiations at Rambouillet, near Paris.

The Serb delegation has insisted both sides should sign a formal statement of principles - a demand which Mr Cook says is delaying proper discussions on a peace settlement.

The BBC's Paul Royall: "Talks are still struggling"

"I delivered a very firm message to President Milutinovic that we have got to get beyond this and get down to real negotiation," the foreign secretary said.

"A statement of principles without a real agreement to the political settlement would be worthless."

Albanians warned

Mr Cook, who visited the talks with his French counterpart Hubert Vedrine, also reminded the Albanian delegation that continuing progress was needed from them if they wanted a Nato force to be sent to implement any peace deal.

Albanian delegates seek a referendum on independence for Kosovo

British tanks and artillery are to be sent to the Balkans next week, ready to join a peacekeeping force if a deal is signed.

But Russia has said that US threats of airstrikes against the Serbs if they allowed the talks to fail, were unacceptable.

So far, the talks have stalled over the failure of both sides to sign up to even an initial peace agreement.

The Serbs are reportedly ready to sign a set of basic principles that include

• preserving the territorial integrity of Yugoslavia
• a ceasefire in Kosovo
• the amnesty and release of ethnic Albanian prisoners.

This would mean the ethnic Albanians renouncing their goal of independence for Kosovo, something they are unlikely to agree to.

International mediators believe that the Serbs' list of principles is unnecessary, since merely by attending the talks, the two sides have already agreed a set of basic principles drawn up by the international Contact Group.

The Albanians are seeking:

• a referendum on independence
• an immediate ceasefire
• Nato guarantees for the eventual interim settlement.

Thousands at funeral

In Kosovo, thousands of ethnic Albanians have attended the funeral of 40 compatriots, killed by Serbian police in the village of Racak last month. The head of the international monitors in Kosovo, William Walker, told their families the killings were a crime against humanity.

At the same time, monitors say they are investigating reports that unknown attackers have abducted two Serb police officers near the northern town of Vucitrn.

Last month, rebels of the Kosovo Liberation Army (KLA) held five Serbs captive in the same area, releasing them two days later.

Year of fighting

More than 2,000 people have died and hundreds of thousands been left homeless in a year of fighting between Kosovar Albanian separatists and Serbian security forces in Kosovo.

The rival sides came to the peace conference when Nato issued an ultimatum: If they refused to attend, the alliance would strike Yugoslavia, and there would be toughened measures to cut off weapons and financing to the rebels.