A Downing Street spokesman denied the soldiers would form any part of a growth in ground forces for a possible invasion of Kosovo.

Details of the deployment are to be announced by Prime Minister Tony Blair in a Commons statement at 1530BST.

Mark Laity reports: "We know the kind of troops they will be"

Other Nato members are expected to announce similar reinforcements in a series of linked statements.

The additional troops will join the 4,000 already in the region. They are stationed in Macedonia and are equipped with 14 Challenger main battle tanks, 40 Warrior armoured fighting vehicles and six AS 90 self-propelled guns.

The news came as Serb radio reported that an RAF Harrier had been shot down over Bosnia and its pilot killed. The Ministry of Defence has categorically denied the report.

The Harriers have been bombing Serbian communication networks, striking at two radio relay stations in Kosovo and Serbia as well as attacking fuel depots.

British troops

At the daily Ministry of Defence briefing, Foreign Secretary Robin Cook confirmed the deployment of more troops.

Nato insists the refugees must be allowed to return under an international force

''These extra resources that we are sending to the theatre also help us plan for success. When the time comes for the refugees to return we will be ready to give them the international protection they will need," he said.

Sir Charles Guthrie, Chief of Defence Staff, said that although the Nato force (Kfor) would pack a "significant military punch" it was not intended as a fighting or invasion force.

"We learned the lesson from Bosnia that a peace implementation force has to be both credible and capable of defending the peace. Kfor is designed for this purpose," he said at the MoD briefing.

Jon Sopel reports: "There could be other similarly linked announcements"

Mr Cook revealed that three times as many Nato planes took part in bombing raids overnight than in previous attacks with RAF Harriers and Tornados fully involved.

He said the stepped-up bombing was a sign to Yugoslav President Slobodan Milosevic that Nato's resolve was strong.

Rejection of fascism

Mr Cook said: ''If President Milosevic had hoped the Alliance would grow weary of the struggle or show a split in its members he must be a very disappointed man this morning.

Tony Blair could hear voices of dissent from both sides of the Commons

''If he is ready to meet our objectives he can have peace today, but if it is going to be a long haul then Nato has demonstrated that we have the political unity and the military strength to see it through.

''The firm foundation for that Alliance unity is our common belief that the arrival of fascism that we have witnessed in Kosovo must have no place in modern Europe.

''Nato was born in the aftermath of the defeat of fascism and genocide in Europe. Nato will not allow this century to end with a triumph for fascism and genocide.''

The foreign secretary said Nato had seen "fresh evidence of brutal atrocities" carried out by Yugoslav forces in Kosovo. There were also reports, he said, of ethnic Albanian women being "systematically" raped in an Yugoslav army camp at the town of Djakovica in southern Kosovo.

Commons statement

Mr Blair will update MPs on the Nato offensive following calls for an emergency Commons recall during the Easter break to debate the bombing campaign.

He can expect tough questioning from those who will query the length of the campaign and growing reports of civilian casualties.