The announcement by the Albanian Foreign Ministry came as Nato raised the pressure on Yugoslav President Slobodan Milosevic on Sunday by blasting Kosovo capital Pristina in a dayight raid.

In an interview with CNN, the Yugoslav Foreign Minister, Zivadin Jovanovic, accused Albania of carrying out aggression against Yugoslav territory in Kosovo and said there was no purpose in maintaining relations.

Mr Jovanovic said there were permanent attacks across the border by the Albanian army and Kosovo Albanian rebels. He also said large quantities of military equipment were being smuggled into Kosovo.

'Heavy bombardment'

The BBC's Kevin Connelly: "A major blow in the campaign"

Serb media reports said three powerful explosions were heard north west of Pristina at around 1310 (1110GMT), while several more blasts followed around two hours later.

The attack follows an overnight onslaught on targets including Yugoslavia's second city Novi Sad. An oil refinery was hit in the industrial town in attacks which Serb media called the heaviest yet.

The refinery at Novi Sad burns

Other targets included chemical plants and key areas of Yugoslavia's industrial and transportation infrastructure in.

A pall of black smoke loomed over Belgrade after Nato hit three plants in a nearby industrial area.

Nato said in one mission all of the 36 planes involved had found targets - and 13 military vehicles inside Kosovo had been destroyed.

(Click here for a map showing recent Nato strikes)

The first US Apache attack helicopters are expected in Albania shortly for deployment against Yugoslav military forces in Kosovo. Meanwhile, five Kosovo Albanian refugees including three children were killed when their car hit a landmine in the no-man's land between a Serbian check-point and the Albanian border.

Serbian troops were also reported to have shelled a line of refugees, killing one and injuring 22 at the same border crossing at Morina.

The BBC's Jeremy Bowen: "More compelling evidence of war crimes"

More than 23,000 Kosovo Albanians passed into Albania on Saturday, taking the total to around 375,000. The total number of refugees who have left Kosovo since the crisis began in March last year is around 735,000.

Suspected mass graves

Refugees are still flooding out of Kosovo

Nato said on Sunday it had aerial photographs of 43 suspected mass graves in Kosovo.

Military spokesman Brigadier-General Guiseppe Marani said the alliance also had evidence that Kosovo Albanians had been forced to dig the graves of their countrymen.

Nato also said it believed a notorious Serb militia known as the Tigers was operating around the town of Pec in western Kosovo as part of a new wave of ethnic cleansing.

Arkan: Wanted for crimes against humanity

The Tigers are thought to have been responsible for some of the worst cases of ethnic cleansing and mass rapes during the 1992-1995 war in neighbouring Bosnia.

Their leader, Zeljho Raznatovic or 'Arkan', has been indicted for crimes against humanity by the international war crimes tribunal in The Hague.

'No plans for invasion'

Meanwhile, UK Foreign Secretary Robin Cook has denied a press report that Nato plans to invade Kosovo by the end of the month.

The Observer newspaper quoted a senior sources in London and Washington as saying that 80,000 troops had been earmarked for the operation. But Mr Cook said the alliance had no plans to send in ground troops.

He told GMTV: "Even if we were now to develop such intentions - and we have not - it would be two to three months before we could act upon it because you will need to assemble an area for a very large force capable of carrying out an armed invasion against resistance.

"Now we don't have two or three months to wait. That is why our response to President Milosevic's activities in Kosovo has been to intensify our present military air campaign."

Nato's Secretary General, Javier Solana, said the alliance believed their air campaign was sufficient right now.

"We're going to see this campaign through," he said on BBC One's Breakfast with Frost. "At this point we think that the campaign is enough ... and therefore we're not going to change the policy now.

"But if the moment comes when it is necessary, I'm sure the countries that belong to Nato will be ready to do it."

US President Bill Clinton has said there will be no peace in the Balkans until Yugoslav President Slobodan Milosevic is removed from power.

Humphrey Hawksley reports: Clinton is "committed to freedom and human rights"

In an article published in the London Sunday Times newspaper, he said he still believed that the best answer for Kosovo was autonomy, not independence.

He said: "Realistically, the realization of this vision will require a democratic transition in Serbia itself, for the region cannot be secure with a belligerent tyrant in its midst."

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