He is one of four European foreign ministers in the province on Wednesday to review progress in restoring peace.

As the politicians toured the region, the Swiss Government announced it had frozen the assets of Yugoslav President Slobodan Milosevic and four other war crimes suspects.

It said the move was at the request of the International Criminal Tribunal for former Yugoslavia.

Mr Cook travelled to the village of Velika Krusa to observe a scene of mass killing being investigated by a UK forensic team for the tribunal.

He told the BBC that he felt "horror that anybody could carry out acts of such barbarity".

"Those responsible must be held to justice," he said.

James Robbins reports: "Mr Cook was spared nothing of the detail"

He praised British forensic teams gathering evidence at the site, and said "the evidence must be watertight" to prepare for future war crimes tribunals.

Mr Cook said the events at Velika Krusa had been ordered and co-ordinated by someone in Belgrade.

"It's very important that we should go to the top of the chain of command and hold them responsible," he said.

First visit from West

Mr Cook and the French, German and Italian foreign ministers are the first senior Western politicians to visit Kosovo since the end of the Nato bombing campaign.

They were due to meet senior international officials and ethnic Albanian leaders, and visit areas of the province patrolled by troops from their respective countries.

French Defence Minister Alain Richard began by visiting French troops in Kosovska Mitrovica.

The BBC's Barney Mason in Velika Krusa: "A hushed, sombre scene"

He said the main task of the French force was to ensure the security of both Serbian and ethnic Albanian populations in the French northern sector.

"We have to make sure they can live where they want and in safety. It is not down to us to make them live right next to each other," he said.

A message for both sides

Cook: "A vision of hell"

Mr Cook delivered a similar message. He said Kosovo Albanians had "an exciting chance to break out of the cycle of violence" and build a democratic, self-governing Kosovo.

He also appealed to Serbs not to flee the province, saying: "You don't need to leave. The peacekeeping force is here to protect you as well."

Robin Cook: "This is complete horror"

However, he faces a stiff task convincing the Serbian minority, which is increasingly bitter and fearful. Many Serbs are terrified of reprisals by the Kosovo Liberation Army.

Russia considers more troops

As the European ministers headed to Kosovo, Russian Defence Minister Igor Sergeyev said Russian paratroops could fly to the province on Monday to bolster Russia's existing 200-strong contingent, subject to a parliamentary vote.

Mr Sergeyev is to discuss the deployment with the Duma and with Foreign Minister Igor Ivanov.

On Thursday he will appear before senators, some of who strongly oppose Russian involvement in Kosovo.

'Revenge' attack

On Tuesday, two elderly Serb civilians were attacked and killed in their homes in the town of Prizren, apparently by ethnic Albanian civilians armed with an axe.

Paul Wood in Pristina: Every day there are more innocent victims

Both bodies had been badly mutilated by the time German K-For troops arrived on the scene. One eyewitness said the woman had been virtually decapitated.

The motive appears to be revenge for what happened to ethnic Albanians at the hands of the Serbs during the conflict in Kosovo.

Now, some 50 Serbs - most of them elderly - have gone into hiding, under armed guard from K-For troops.

(Click here to see a map showing refugee movements)

With the air war now over, fighter jets and other US warplanes sent to Europe as part of the allied bombing campaign are beginning to pull out.

Ten British Harriers based in Italy for the conflict flew home on Tuesday.

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