As the alliance delivered a more cautious estimate of the quantity of oil remaining at the disposal of the Serbian military, Nato's supreme allied commander, General Wesley Clark, pressed for tough new rules of engagement which would allow the search of vessels arriving in Montenegro.
That plan, along with a separate study on the possible bombardment of a pipeline inside Montenegro, will be debated by Nato's political chiefs at a meeting of the North Atlantic Council today. If given the go ahead, the stop and search regime could bring the alliance into conflict with Russia which has said it will ignore the oil embargo.
However the alliance's concern over the quantity of oil still arriving in Serbia was underlined by an assessment from General Clark that 10 ships are arriving each day at the port of Bar, and unloading 24 hours a day. That compares with the two or three vessels which docked at the Montenegrin port before the air bombardment.
Although Montenegro is a part of the Yugoslav republic, it has stayed out of the conflict and Nato has been unwilling to make it a military target.
The alliance, which has previously claimed to have destroyed 70 per cent of Belgrade's refining capacity, yesterday produced a different and less impressive statistic, claiming that 33 per cent of Serbia's military oil reserves had been eliminated.
With the concentration on the need to block off more oil, General Clark said "any visit and search regime has, of course, to have appropriate rules of engagement to be able to use the threat of force". He added that "if it is approved [by the Nato ambassadors] the officers dealing with the merchant ships will give them appropriate instructions."
The alliance hopes that merchant ships will contact them to seek clearance for cargoes sailing into the area. But a Nato source suggested that, under international law, Nato naval commanders would be allowed to board and search all vessels, including Russian ones, and - if they were found to be carrying oil - warships would be able to escort them to port.
With a new point of conflict with Moscow looming, there was added gloom within the alliance at the lack of progress on the diplomatic track during talks held by the US envoy, Strobe Talbott, in Moscow.
The former Russian prime minister, Viktor Chernomyrdin, said that Belgrade had agreed to an "international presence" in Kosovo with Russia's participation, but he acknowledged that such a group, which would be only lightly armed, was well short of Nato's demands. "Nato thinks that primarily its forces will participate [in Kosovo]. It will take time to work out this issue in detail," he added.
Nato officials say that the international force could include Russians and Ukrainians, as well as troops of other nations which have taken no active part in the air campaign, such as Greece. Their presence is seen as an advantage because it could reduce the risk of attack from remaining Serb forces. But Nato diplomats are insistent that the force must be under Nato command and control, rather than be of the type that was humiliated in Bosnia.
One diplomat argued: "Its existence could be covered by a UN resolution, but it is not going to be a blue helmet operation." Nato's planning is based on the assumption that its missions will include the force lead by General Sir Mike Jackson, the Commander of the Allied Command, Europe, Rapid Reaction Corps, which is currently based in Macedonia.
Yesterday General Clark reiterated his conviction that the air campaign is being successful, arguing that it is eroding Yugoslav morale, leading soldiers to desert and encouraging draft-dodging. "We're picking up an increasing numbers of desertions and declining morale among the troops."Reuse content