Operation Allied Harbour will begin by the end of next week, said spokesman Jamie Shea.

The decision was announced as Nato Secretary-General Javier Solana warned that Serbian troops might use Kosovo Albanian refugees as human shields.

Fears are growing that Serbs are forcing refugees home

As Yugoslavia counted the cost of Nato's 15th night of bombing, Nato said it would attack Serb transmitters unless Western programmes were given several hours' airtime in Serbia.

Spyros Kyprianou, speaker of the Cyprus parliament, flew to Belgrade on Thursday to secure the release of three captured American soldiers.

The Pentagon earlier said it was believed the men would be handed over and flown to Cyprus on Thursday night.

Click here for a map showing Nato's latest strikes

But the Greek Cypriot politician is now staying overnight in the Yugoslav capital after Serbian deputy prime minister Vojislav Seselj reportedly said the liberation of the soldiers was out of the question. It was reported that Mr Kyprianou hoped to meet Yugoslav President Slobodan Milosevic on Friday.

Miodrag Popovic: "Refugees will be safe from Nato bombardment"

Miodrag Popovic, Serbian Deputy Information Minister, told BBC News 24: "How can Nato expect a goodwill gesture when they are killing Serbian civilians?"

Reports say 25-30,000 refugees trapped in Kosovo are being forced back to their homes after Serbs closed down border crossing points on Wednesday.

Fergal Keane reports: "When you cut through the political rhetoric - this is ethnic cleansing"

A further 10,000 refugees, missing following the forced evacuation of the Blace camp on the Macedonian border, have been traced.

The United Nations High Commissioner for Refugees says they have been found either in Albania, or on their way there.

Human shields warning

Mr Solana suggested the Yugoslav president could be trying to stop the images of people fleeing Kosovo, or that there could be a more sinister explanation.

He said: "I think he would probably like to stop these images being seen and also, perhaps, use the people who are in Kosovo as shields, probably against the air strikes."

UK International Development Secretary Clare Short said the forcible movement of people was completely unacceptable.

She said: "He (Milosevic) and his henchmen will be held fully responsible for any harm that comes to the Kosovars at the hands of his troops and paramilitaries. They will be held accountable for war crimes."

The Yugoslav government has insisted that international aid agencies can have unfettered access to Kosovo to monitor the return of the refugees and declared the Kosovo Macedonia crossings open.

And in a statement on Serbian radio, the government said its security forces had ended what it described as anti-terrorist operations in Kosovo.

However, Serb forces have been seen laying mines along the border between Kosovo and Albania.

German Defence Minister Rudolf Scharping said on Thursday that dozens of Kosovo Albanians had been massacred in the previous 24 hours.

He said 35 unarmed civilians had been assassinated in the village of Sopi and that a massacre had taken place in Pastric.

He did not give details of the source of his information, but said proof would be available on Friday.

As the bombing campaign continued, Knut Vollebaek, chairman of the Organisation for Security and Co-operation in Europe (OSCE), travelled to Moscow for talks with the Russian authorities to find a diplomatic solution to the conflict.

Russian Foreign Minister Igor Ivanov said that diplomatic efforts to resolve the Kosovo crisis were making some progress.

'Pristina in ruins'

In Kosovo, western journalists were allowed the first controlled access to the provincial capital, Pristina.

The BBC's John Simpson: "Nobody thought that Pristina could become this shell of its former self"

They reported that parts of the city were in ruins and the streets deserted apart from packs of dogs, paramilitary police and a few elderly people. The city had a population of 250,000 before the start of the conflict.

With Serb forces still active, US Secretary of State Madeleine Albright on Thursday defended herself amid accusations that she had underestimated Yugoslav President Slobodan Milosevic's resolve against Nato air strikes.

US Defence Secretary William Cohen is in Germany for a meeting with counterparts from Britain, France and Germany to discuss the air strike strategy.

In the overnight bombing, two loud explosions, both of which could be heard from several miles away, rocked central Belgrade's government quarter.

Defiant: Serbs in Belgrade

Up to 3,000 Serbs defied the bombs by attending a concert at Belgrade's principal bridge - a suspected Nato target.

City residents attending the rock concert - aimed at preventing Nato strikes - were shown on state television standing defiant.

John Simpson reports from the war torn city of Pristina

But Pentagon spokesman Rear Admiral Thomas Wilson said such action by volunteers would not protect targets from Nato action.

He also told a media briefing that Nato's campaign was severely disrupting Serbian transport routes and fuel supplies.

He said vital oil refineries had been put out of action and a number of bridges had been destroyed or damaged.

Targeted: Kosovo capital Pristina

European Union foreign ministers meeting on Thursday closed ranks behind Nato's air raids, calling them "necessary and warranted".

Ministers said military action was necessary "in the face of extreme and criminally irresponsible policies" and repeated violations of UN resolutions.

They also held out the prospect of EU membership to Albania and Macedonia.

• Blair: No troops for Kosovo
• Pristina - a deserted city
• Serb media a 'legitimate target'
• Analysis: Nato's air campaign moves up a gear
• Serb TV: Nato's mission impossible