Bosnian Serbs flee Muslim vengeance: Muslim fighters are winning back areas of Bosnia 'cleansed' last spring and even threatening Serbia itself. Robert Block reports from Grabovica

MUSLIMS are burning Bijelovac a few houses at a time. Every day for almost a week the Muslims have come down from their bases in the Bosnian mountains and set fire to bits of the small village on the western bank of the Drina river, no more than 300 yards from Serbia. From Grabovica, directly across the river on the Serbian side, you can easily make out each house on fire.

On Sunday evening four women stood at the roadside in Grabovica, watching the flames jump high into the air and consume houses they knew well.

'We recognise the houses that are burning,' said Nevenka Simic, 29. She pointed to a charred building next to a smouldering house. 'You see there. No, not the house with smoke. The white one with black walls; that was my house.' She paused. 'If it was only the house I lost. Much of my family has been killed.'

Mrs Simic said that in the fighting for the village last week she lost her mother-in-law, two uncles and a grandfather. At least 109 Serbs are said to have been killed by Muslim forces in Bijelovac.

Serbs are suffering from a post-ethnic cleansing hangover: a violent backlash of revenge killings by Muslims which reflects the changing balance of the war.

Increasingly effective small groups of Muslim guerrillas have started to retake a swathe of territory in south-eastern Bosnia along the Drina river, which separates Bosnia from Serbia. This is the area which Serbs rolled through and 'cleansed' at lightning speed in April and May. But since 15 December Muslims have been fighting back. They rule the mountains and are attacking Bosnian Serb positions from Zvornik to Foca.

Muslims control several villages along the western bank of the Drina - from outside Bratunac, which they are still fighting to take, to just beyond Bijelovac. From here they fire into Serbia. Serbs displaced from villages in Bosnia talk about Muslim threats to cross the river and raid Serbian villages and towns.

In Grabovica, just south of the Serbian town of Ljubovija, Miloje Mitrovic's barn is testimony to the ease with which the Muslims can now reach into Serbia proper. Last Tuesday, a Muslim bullet hit the barn, setting it on fire. On Sunday, the smell of burned wood and grain still hung in the air. Mr Mitrovic, 73, managed to save all but the roof. But he can no longer work the field which straddles the river bank in front of his house for fear that he will be shot. 'Even soldiers won't patrol there,' he said.

There are only a handful of Yugoslav army soldiers visible along the 20km or so from Zvornik to Grabovica. Last week, Mr Mitrovic said, the army left some weapons at the local school for anyone who wanted them, but that is all.

In November, Bratunac was bristling with guns and tough Serb fighters as it reluctantly allowed a UN relief convoy to get through to Srebrenica, whose Muslim residents had been cut off from the world since the Bosnian war started in April. Most Serbs believe that aid gave the Muslims the strength to fight again.

One refugee, Mitra Ilic, 46, arrived in Ljubovija on Saturday from Mandica with her youngest son and just the black 'Top Gun' bomber jacket on her back. Her husband was killed in a Muslim attack on Monday. She said she fled after Serb fighters arrived at the village late on Friday night ahead of another Muslim attack, telling women and children to flee.

Watching the burning houses in Bijelovac, Mr Mitrovic pointed across the Drina. 'That was all Serb territory before the Muslims came. It was brutal the way people were killed. It's worse than during the Second World War. I cannot remember such shooting and burning like there is now. It's revenge. Just revenge.'

(Map omitted)