With the alliance struggling to agree the terms of its stop-and-search regime, diplomats have switched tack, arguing that a large number of tankers could be stopped without a full-scale confrontation with Russia.
The alliance says that, with many countries already committed to the terms of the embargo, most tankers will automatically be prevented from delivering cargo. All European countries have agreed and EU applicant countries, including Cyprus and Malta, have also agreed to sign up.
Also on board are the US, Canada and most East European states, and many Islamic countries, including Malaysia and Indonesia. For all these countries the stop-and search regime will be straightforward and easily enforceable, the alliance believes.
Nato chiefs concede there are loopholes, such as tankers sailing under flags of convenience. However, many of these will, they believe, be prevented from sailing by the risks of entering that part of the Adriatic, and by the rise in insurance premiums for vessels.
Russia remains the most difficult problem because it has not signed up to the embargo, and Nato's right under international law to stop and search Russian ships is highly questionable.
Yesterday Moscow repeated that it would take no part in the ban, despite Western warnings of "serious consequences" facing any country that ships oil to Belgrade.
Russia's Foreign Minister, Igor Ivanov, said: "Russia is not a country that can be threatened, as [the US Defense Secretary] William Cohen is doing. I don't consider it reasonable to slide into a policy of threats, which would lead nowhere."
Nato has been stung into action because of Belgrade's continuing access to supplies via the Montenegran port of Bar. One alternative tactic that may be deployed by the alliance is to target roads and other supply routes inside Montenegro.
Last week the Supreme Allied Commander Europe, General Wesley Clark, appealed for tough powers to stop and search, but efforts to reach an agreement on the terms of engagement have been delayed in Nato's Military Committee because of disagreements.
The final decision will have to be taken by Nato ambassadors sitting in the North Atlantic Council, possibly over the weekend.Reuse content