Several thousand frightened civilians were last night trapped on a freezing Kosovo mountain road by a Serbian offensive close to the border with Macedonia.
As skirmishes broke out elsewhere, international monitors feared an escalation into full-scale war which could scupper the chances of the new peace talks due to start in France in two weeks.
In the most serious incident of the day Serb forces attacked the town of Kacanik after they were themselves attacked by rebel guerrillas who fired on a police station in a nearby hamlet killing a policeman and wounding four more.
As Serb forces drove into the town from the north, several thousand ethnic Albanian men, women and children fled to the south, along a mountain road towards the nearby border with Macedonia.
But they found their way blocked by more police, who then closed the border, refusing to allow international monitors reach the terrified civilians.
"Two or three thousand villagers fled Kacanik and Gajane and tried to cross into Macedonia but were stopped by the border police," said a spokesman for the international monitors of the Organisation for Security and Co-operation in Europe (OSCE).
Last night several hundred villagers, some with babies, were reported to be clustered close to the border post of Gen Jankovic, with more people huddled back along the highway.
Meanwhile, to the north, Serbian tanks attacked rebel positions near the town of Vuciturn, the latest stage of an on-off offensive that is gradually pushing the guerrillas of the Kosovo Liberation Army out of fortified positions in nearby hills.
And, to the west, British monitors were trapped in a police station by an angry Serb mob after rebels took two Serbs hostage near the town of Orahovac.
The Serbs, snatched while cutting wood in a nearby village, are apparently being held as bargaining chips to secure the release of three ethnic Albanians taken hostage last week in Orahovac.
The monitors and local police persuaded the mob to disperse, but there were fears yesterday that unless the two hostages are released the Serbs would carry out a threat to attack nearby KLA positions with troops now positioned outside the town.
One monitor near Orahovac said Serbian forces were now sending columns of armoured vehicles through rebel-held areas, with observers racing ahead of them to persuade guerrilla units to hold their fire.
"The army are always trying to provoke them. They are going down there with their tanks," said one monitor watching from hills above the nearby town of Suva Reka.
But guerrillas too are on the march. One senior KLA officer told monitors yesterday that the guerrillas consider they are now strong enough to hold their own in future fighting and he showed little interest in the planned peace talks.
"That's dangerous thinking," said one monitor. "They can't take on the Serbs."
Last spring the KLA expressed similar sentiments - only to see Serbian forces smash their defences, driving 200,000 refugees from their homes throughout central Kosovo.
Two ethnic Albanians were killed and one was wounded late yesterday in a shooting incident in the centre of Pristina, capital of the Serbian province of Kosovo, police said. Witnesses said unknown persons in a car opened fire on an Albanian-owned cafe. An informed source said it looked like a settling of accounts between ethnic Albanians.