Provisional measures authorising naval forces to board and search suspect ships in the Adriatic will be approved by the Nato council in the coming days.

The embargo was part of a statement issued by Nato on Friday as it met in Washington to mark its 50th anniversary.

However, a British official said the plans fell short of a blockade.

The BBC's Kevin Connolly: Drying up Yugoslavia's oil supplies is a Nato priority

According to BBC Washington correspondent, Paul Reynolds, they are a compromise between the Americans, who want a full-scale naval blockade, and the French, who argue that this would be illegal without UN authorisation.

The search procedures are not yet comprehensive - for example, what happens if a ship defies patrols in the Adriatic has not been decided.

US troops and firepower are on their way to protect Apache helicopters in Albania

Confrontations are possible if Russia - Belgrade's main oil supplier - seeks to deliver oil to Yugoslavia.

"Nato would be extremely foolish to enforce a ban as it would lead to direct confrontation with Russian civilian vessels," said Ruslan Nickolov, a London-based oil analyst.

Before the crisis in Kosovo, Serbia had to import 54,000 barrels of oil a day, mainly from Russia and Greece.

Oil targets

Nato air strikes targeted oil refineries in the northern city of Novi Sad and Pancevo overnight on Friday in a drive to cut off fuel supplies to Serbian troops.

(Click here to see map of last night's Nato strikes)

Michael Williams reports from Belgrade: "Local sources calim damage to residential areas"

The BBC's correspondent in Belgrade, Mike Williams, said flames from Yugoslavia's ever diminishing oil reserves lit up the night sky in Novi Sad.

And the night of intense bombardment has inflicted what Serbian authorities said was immense damage on the southern city of Nis.

President Clinton and Nato Secretary-General Javier Solana celebrate the Nato anniversary

Serbian media reports said 26 missiles struck the city in two intense waves of bombing.

They were reported to have hit a factory, a railway shunting yard, a water works and electric power lines.

Local sources said a residential area had also been hit, with one civilian injured.

There were also strikes against the Kosovo capital, Pristina, with heavy damage to Slatina airport and the communications tower on Mount Goles among others.

The BBC correspondent says many of these places have bee hit time and time again, helping to confirm the widely held view among Yugoslav citizens that despite its denials, Nato is trying to make life as difficult as possible for the people of Serbia.

'Nato will prevail'

According to Nato, the oil embargo and other economics sanctions are part of an attempt to intensify pressure on the Yugoslav President Slobodan Milosevic.

A seventeen-point statement on Kosovo was issued at Nato's 50th anniversary summit in Washington emphasised that Nato will prevail over the Serbian leader,

Nato leaders said air strikes would continue until Yugoslavia met all their demands over Kosovo.

Reinforcements expected

As the war of words escalated, the US announced plans to send 15 tanks to Albania to help protect the newly arrived Apache helicopters.

The tanks will join 2,000 extra troops, and further supplies of rocket launchers and artillery being deployed in the region.

According to the Pentagon, the new fire power was requested by Nato's Supreme Commander, General Wesley Clark.

Serbia hampers Montenegro imports

Montenegro says Serbian forces are trying to prevent imports of medicines and other humanitarian aid entering the country through the port of Bar, on the Adriatic coast.

Although Montenegro forms part of the Federal Republic of Yugoslavia, the republic does not support President Milosevic, and supplies are not being passed on into Serbia.

But the Yugoslav army and navy maintain a strong presence around the port, and are able to police the embargo by threatening to confiscate any imports not authorised by Belgrade.

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