His comments came as international monitors sent to the trouble-torn province five months ago to verify a now-defunct ceasefire were pulling out to neighbouring Macedonia.

Diplomats were also being pulled out of Belgrade, and the UK, French and Polish governments advised their nationals to leave Yugoslavia as the prospect of a military response to the crisis loomed.

Robin Cook: "It is a very grave situation"

Mr Cook described the situation following Friday's collapse of peace talks in Paris as "very grave" and said Nato was now preparing to unleash its air armada against the Serbs.

"If there is no progress, then we are looking at a time scale of a matter of days in which action can begin. Those preparations are now under way," he told BBC Radio 4's Today programme.

International monitors leave Kosovo

"How long it will continue will be very much down to President Milosevic. The only way out is to come to the table and agree to the peace package."

Mr Cook blamed the collapse of the talks, brokered by the six-nation contact group, firmly on the Serbs who have been refusing to accept a Nato peacekeeping force to police a settlement.

"We suspended the talks yesterday because in truth the Serb side were showing no serious commitment to negotiations and were plainly filibustering," he said.