Mr Cook was speaking in the capital, Pristina, where he was given an enthusiastic greeting by several hundred people.

Earlier in the day he visited the site of an alleged massacre of Kosovo Albanians, together with the foreign ministers of Germany, France and Italy.

The ministers were shown a burned-out building at Velika Krusa in south-western Kosovo, where more than 100 people are believed to have been set on fire and shot dead.

Robin Cook: "This is complete horror"

After seeing the remains of some of the victims, Mr Cook described it as a "vision of hell".

Meanwhile, the International Committee of the Red Cross has asked the Yugoslav authorities for access to a number of Kosovo Albanian political prisoners being held in Serbia.

More pressure on Belgrade

Yugoslav President Slobodan Milosevic has come under more pressure from the international community.

The Swiss Government announced it had frozen his assets and those of four other war crimes suspects.

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

The BBC's James Robbins: "Cook could see straight away the evidence of horror"

Albania has said it wants no further contact with Yugoslavia while President Milosevic remains in charge.

Closer to home, 74 university teachers from Montenegro published an open letter calling for independence from Yugoslavia.

US Marines run for cover after the incident at Zegra

Montenegro's President Milo Djukanovic has already threatened to call a referendum on independence.

In another development, US marines manning a checkpoint in Kosovo shot dead one person and wounded two others.

The men fired into the air and then pointed their guns at the Marines, at which point they were gunned down.

All three were in civilian clothes, and the Americans say it was not clear whether they were Serb or Albanian. There were no American casualties.

A message of peace

At a news conference in Pristina, Mr Cook said the EU foreign ministers had urged representatives of the Kosovo Albanian community, the KLA and the Serb Orthodox church to "use the new freedom to build an open society and to provide a prosperous and peaceful future."

Joschka Fischer was shaken by the evidence

The foreign ministers had assured the Serb Orthodox delegation K-For would protect all ethnic groups in the province, Mr Cook said.

"We want to see a multi-ethnic and multi-religious Kosovo. Let us break the cycle of violence," he said.

After seeing the site of the alleged massacre at Velika Krusa, Mr Cook said he felt "horror that anybody could carry out acts of such barbarity".

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

'Need for watertight evidence'

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

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.

The visibly shaken German Foreign Minister, Joschka Fischer, reiterated Mr Cook's words after seeing the site.

"I think that those responsible must stand before the court," he said.

The foreign ministers were the first senior Western politicians to visit Kosovo since the end of the Nato bombing campaign.

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

(Click here to see a map showing refugee movements)

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.

Ben Brown reports: "The two communities are living in fear of each other"

"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.

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

Meanwhile the true cost of the war is becoming clearer. A group of independent Yugoslav economists has estimated the country will need $29bn over the next five years to repair damage done by Nato bombs.

• Switzerland moves against Milosevic
• Be patient, Clinton urges refugees
Russians accused of Kosovo atrocities
• Eyewitness: Investigating the killing
• Eyewitness: Kosovo's divided communities

Mr Clinton: Revenge "will not satisfy anyone and it will only compound the horror"