With refugees fleeing across the border into northern Albania, the Albanian Prime Minister, Fatos Nano, accused the Serbian authorities in Kosovo of pursuing a deliberate policy to drive out the majority ethnic Albanian population.

He said the violence could lead to war if it was not halted.

The Albanian government says 2,000 refugees have arrived since the start of the weekend.

The influx comes amid reports of intense fighting on Sunday, in which Serb police said they killed dozens of ethnic Albanians fighters.

A spokesman for the United Nations Refugee agency, Tam Meechu Bot, said several thousand more ethnic Albanians were reported to be on the move.

Difficult to return

The Albanian interior ministry says it is by far the biggest wave of refugees since Serbian security forces in Kosovo began a major offensive against armed ethnic Albanian separatists at the end of February.

A spokesman, Artan Bizhga, said the refugees were mainly women, children and the elderly, many of whom had walked for as many as 10 hours. They were being accommodated in local homes and a school, and local authorities were providing free food and clothes.

BBC correspondents say that most ethnic Albanians are afraid to flee because of the difficulty in returning to their homes once they have left.

The border between Yugoslavia and Albania has officially remained closed since last year's uprising against the former Albanian President, Sali Berisha. It is also tightly guarded by the Yugoslav army in an attempt to keep out Kosovo Liberation Army reinforcements.

• More than 250 people have been killed in clashes between Serbian police and ethnic Albanians since the beginning of the year

• 90% of Kosovo's population of 2.2 million are ethnic Albanians, most of whom seek independence from Serbia

• Serbia stripped the region of its autonomy in 1989 and has ruled it since with a heavy military and police presence

Nato dilemma

Last week, Nato announced a series of measures to heighten its military presence in Albania and Macedonia, with a veiled and indirect threat of military intervention in Kosovo itself.

Nato spokesman: nothing is ruled out

As the fighting continued, a Nato spokesman, Nichaloas Firenze, said that no action had been ruled out.

But the BBC Defence Correspondent says that Nato is unlikely to intervene because Kosovo is officially part of another country - Serbia - and therefore the legal basis for an intervention would be questionable.

BBC Defence Correspondent: Nato is 'fated to be a spectator on the sidelines'

Our correspondent says that if Nato chooses to contain the situation from the border, it could risk blocking the escape routes of ethnic Albanians, and thus inadvertently supporting the Serb forces.