Mr Robertson told Members of Parliament that the UK was "determined to play its part in supporting a negotiated settlement in Kosovo".

But he added: "We will only deploy our forces in support of an operation with a clear mission and clear objectives - and alongside our allies."

The contingency plans, he said, did not pre-judge the results of the current peace talks between the two sides taking place near Paris.

The BBC's Keith Breene: The plans represent considerable British commitment

Mr Robertson said 200 soldiers would go to Nato bases in Greece and the former Yugoslav Republic of Macedonia to ensure that heavy equipment needed by British troops - should they be sent - would be in place.

Challenger tanks, armoured vehicles and artillery will be sent to the region on Monday.

George Robertson tells MPs of "prudent" contingency plans

Mr Robertson's announcement comes as peace talks between the Serbian Government and representatives of ethnic Albanians in Kosovo remain deadlocked.

Foreign Secretary Robin Cook has criticised the Serbs for using delaying tactics in the negotiations.

Neither side has agreed to an initial peace agreement despite threats of Nato intervention if the talks, being jointly brokered by the French and British foreign ministers, fail.

Mr Robertson said a news blockade had been imposed on the peace talks in a bid to focus the delegates on the negotiations.

But he said: "It is clear, however, that progress is being made."

Conservative defence spokesman Robert Key backed the government's announcement saying it made "good military sense".

Nato generals are currently working on plans to send 25,000-30,000 troops to Kosovo if a peace plan is agreed.

President Clinton says he is considering sending up to 4,000 US soldiers.