He said those involved in the Kosovo campaign were helping to make the world safer for the 21st century.

His visit to Europe began as Nato suffered its first fatalities since the start of the bombing. Two US Apache crew died when their helicopter crashed during a training exercise in Albania.

Serbian forces have stepped up their persecution of Kosovo Albanians, according to the accounts of refugees leaving the province.

US Defence Secretary William Cohen is likely to recommend the release of two Yugoslav soldiers held by the US "within a few days".

Nato will deploy US F-18 fighter bombers in Hungary shortly.

'Stand for humanity'

Speaking at the Spangdahlem military base, Mr Clinton reminded soldiers that Nato is attacking Yugoslavia to halt ethnic cleansing in Kosovo.

"If we want Europe to be undivided and democratic and at peace for the first time in history... then we must stand in Kosovo for the... humanity of every living breathing, living person in this continent," he said.

"We have no quarrel with the Serb people," he continued.

"Our quarrel is with ethnic cleansing."

In a speech punctuated by cheers and whistles from the crowd, Mr Clinton made reference to the ethnic diversity of the US armed forces.

"I think the US military is stronger because we rally everybody's strength," the president said.

He reiterated Nato's conditions for ending the war:

"The Kosovars must be able to go home safely and with self-government.

"The Serb troops must go home - in their place must be an international force with Nato at its core."

Yugoslav PoWs could be freed

Earlier, US Defence Secretary William Cohen said he would shortly recommend the release of two Yugoslav prisoners of war held by allied forces.

The move comes days after Yugoslavia released three US prisoners of war in response to an appeal by the Rev Jesse Jackson.

Mr Cohen, who is accompanying US President Bill Clinton on his visit to Europe, denied suggestions that the release of the Serb PoWs should be considered a goodwill gesture toward Yugoslav President Slobodan Milosevic for releasing the US servicemen.

Bridget Kendall reports on Clinton's high-profile trip to visit US troops

He told a news conference in Germany that he expected to make his recommendation within days.

The prisoners of war were seized by the Kosovo Liberation Army (KLA) and handed over to the US military.

President Clinton, Mr Cohen, and US Secretary of State Madeleine Albright met Nato officials in Brussels on Wednesday morning.

They were told that Nato was winning in its campaign against Serbia.

After addressing the troops at Spangdahlem, the president is due to go to the Ramstein military base to meet the three US soldiers released by the Yugoslavs.

He will also meet Chancellor Gerhard Schröder - a meeting expected to boost the chancellor's position as his government faces growing public opposition to the war.

Two US airmen dead

Two US airmen are now confirmed dead after an Apache helicopter crashed during a training mission north-east of the Albanian capital, Tirana.

Military officials say the crash will not hinder training operations involving the Apaches.

It was the second Apache to crash in the past 10 days.

They are believed to be the first Nato military casualties in the conflict.

Yugoslav media say Nato aircraft have carried out new attacks in central Serbia, with explosions at Novi Pazar, Kadinjaca and Bajina Basta.

Electricity supplies were cut off in Belgrade.

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

Nato is to base24 F-18 fighter bombers in southern Hungary, according to the country's Defence Minister, Janos Szabo.

It will be the first time Nato attack aircraft for the Kosovo conflict will have been based in the only NATO member state bordering Yugoslavia.

More accounts of abuse

One man shot by Serb police watched two companions die

Increasing numbers of refugees are arriving in Albania and Macedonia, bringing more and more stories of men being taken away and murdered.

Thousands crossed into Albania on Tuesday and more are on their way.

Nato says those fleeing to the province's borders have been "ethnically cleansed" from their homes.

The evidence of physical violence is increasingly a cause for concern.

Many refugees report Serb police demanding money from them. Those who refuse to pay are shot, according to the refugees.

Moving away from danger

The UN refugee agency is considering closing refugee camps in northern Albania and moving people further south, as it fears the refugees may be in danger from Yugoslav artillery fire from across the border.

Duncan Kennedy: Clinton's job is part political, part military

But at the same time, the Albanians may also have to cope with a further influx of Kosovo refugees who have overwhelmed the authorities in Macedonia.

Aid agencies in Macedonia trying to cope with a new influx of Kosovo refugees say they are having to take new measures to deal with security and overcrowding problems.

• Two die in Apache crash
• UK to take 'thousand refugees a week'
• US Senate shelves Kosovo motion
• Politics 'hurt' Nato strikes
• Clinton praises soldier releases
• 'Soft bombs' hit hard