The Security Council was told that such an embargo would further restrict the ability of international humanitarian agencies to provide assistance to civilians inside Yugoslavia.

Sergio Vieira de Mella, the Under Secretary-General for Humanitarian Affairs, acknowledged that most of Yugoslavia's remaining fuel stocks were being diverted towards Belgrade's military effort.

But he added that the planned embargo would be felt first by civilians, not the military.

Mr Vieira de Mella made the warning at a private meeting of the Security Council, which was discussing Nato's air campaign and its humanitarian consequences.

Russian question

Oil supplies are being diverted to the military

Nato decided to impose an oil embargo against Yugoslavia, possibly by means of a naval blockade, to cut off fuel supplies to Belgrade's forces.

General Wesley Clark, the Supreme Commander of Nato forces in Europe, says any oil embargo should be backed up with the threat of force.

But France is among a number of alliance members to have expressed reservations about the plan, saying it would be illegal without a specific UN resolution and could spark a confrontation with Russia.

Russia has warned it will not recognise the embargo and will continue to supply oil to Yugoslavia.

Agricultural difficulties

UN Correspondent Mark Devenport: "Humanitarian aspects of the Kosovo conflict"

At the UN Mr Vieira de Mella told the Security Council that "a fuel embargo would impact the civilian population first, and that the stated objective - an impact on the Yugoslav forces - would take more time".

He said an embargo "would further restrict the ability of international humanitarian agencies to provide assistance to civilians within the Federal Republic of Yugoslavia".