Stephen Sackur: "The French have grave reservations about imposing a naval blockade around the port in Montenegro"

The move comes in the wake of Nato attacks on petrol depots and oil refineries that have significanlty reduced Serbian fuel supplies.

According to Nato spokesman Jamie Shea, the organisation is looking for ways to clamp down on such shipments.

"Our military authorities will be looking into what the options are to screw the tap down still further," he said.

Tankers are able to deliver oil through Montenegro, part of the Yugoslav federation, and barges can also get access to Serbia across the Danube.

The United States Secretary of State, Madeleine Albright, has said that she does not rule out the possibility of a naval blockade of Yugoslav ports.

"We're taking all kinds of steps to limit the ability of outside powers to ... deliver oil," she said.

According to the BBC's Washington Correspondent, Paul Reynolds, the US ran into some opposition within Nato on the grounds that international law should not be broken.

The New York Times reported that the French, in particular, had raised concerns.

The French Defence Minister, Alain Richard, has since said that oil supplies have to be cut off, but the legal basis for doing this is still under discussion.

Oil supplies affect conflict

According to Jamie Shea, the delivery of oil to Yugoslavia by sea or land, while technically legal under international law, would only serve to prolong the military conflict.

"We would hope that all countries of the international community would ... not wish to undertake any action that would prolong this conflict by supplying refined oil to Yugoslavia," he said at a news briefing.

Economic sanctions prohibiting the sale of oil to Yugoslavia were lifted in 1995 following the signing of the Dayton peace treaty ending the war in Bosnia.

And the Nato air strikes have succeeded in diminishing about 70% of the Serbian military's fuel supplies.