Speaking at the daily Ministry of Defence briefing Mr Cook said: "Refugees are going to return and they are going to return under international military protection.

"Kosovo must be made safe for the refugees to return. That is the objective of our military campaign and our diplomatic campaign."

He added that US President Clinton's visit to Germany, where he is meeting Nato Secretary General Javier Solana, symbolised the unity of the alliance and the determination of all member states to "complete the task to which we have set our hand".

Joe Lockhart: US wll back the strikes for "as long as it takes"

Also speaking at the briefing White House spokesman Joe Lockhart revealed that President Clinton will be meeting some of those driven from their homes by the Serbian military on Thursday in order to assess the human cost of the crisis first hand.

President Clinton's visit to Europe comes as Nato has suffered its first fatalities since the start of the bombing campaign against Serbia.

Two US servicemen were killed when their Apache helicopter crashed during a training exercise in Albania.

'Russia will not ride to Serbs' rescue'

Turning to the diplomatic efforts to end the conflict Mr Cook said that as Russian envoy Viktor Chernomyrdin says he is "more optimistic" about a solution to the Kosovo crisis, after meeting President Clinton and United Nations Secretary General Kofi Annan, Yugoslav President Slobodan Milosevic "knows now that Russia will not ride to the rescue".

Mr Cook said further efforts to forge a diplomatic solution would be made on Thursday when the G8 meet in Bonn.

He said if further common ground was found with Russia over sending in an international force into Kosovo, "then the door would be open for UN endorsement of an international force to return to the region".

The foreign secretary and Mr Lockhart both insisted the air campaign was succeeding and was further degrading the Serbian military machine.

A UK military spokesman then gave the latest details on the air strikes saying attacks were continuing on Serbian ground forces, armour and artillery as well as military supplies and infrastructure.

He added that a Serbian air force MiG 29 had been shot down on Tuesday night.