William Walker, American head of the unarmed mission, said his observers had been threatened by Serb police after they tried to reach the latest flashpoint in the town of Podujevo, north of the province's capital Pristina, on Christmas Eve.
"I became more concerned about the security of my people after yesterday's violence," Mr Walker said. He said he feared the violence would worsen and that Serbia would not fulfil its pledge to guarantee the safety of the international observers.
"The evidence I have seen so far shows that the government is incapable of ensuring their safety," he said.
Kosovo's crumbling truce appeared to collapse entirely on Christmas Eve after Serbia sent about 100 tanks into Podujevo in search of Albanian fighters from the pro-independence guerrilla movement, the Kosovo Liberation Army. The KLA killed a Serb policeman earlier this week. Yesterday, one Albanian, a six-year-old girl, was reported killed by Serbian forces, although the death toll is expected to rise.
The assault elicited a declaration from the KLA that theyregarded the American-brokered truce as over.
"The KLA will not stay with arms crossed, [but] will attack and defend itself," the movement said in a statement carried in yesterday's Albanian- language media in the province.
Fighting in Kosovo between local Albanians and the Serbian authorities started in the spring. It slowed in October after Western powers threatened Serbia with air strikes if it did not halt an offensive that drove hundreds of thousands of Albanian civilians from their homes.
The Organisation for Security and Co-operation in Europe then deployed the observers, pending expected talks on autonomy for Kosovo, which show no sign of taking place.
The European Union envoy on Kosovo, Wolfgang Petritsch, warned Serbia yesterday that the West "will not tolerate an excessive use of force by the Yugoslav army" in the province.
"Dozens of armoured vehicles and tanks have been observed deployed in the region," Mr Petritsch said. "Villages close to Podujevo are [being] attacked by heavy artillery".
Nato's Secretary-General, Javier Solana, said the Serb offensive was in "clear violation of the commitments" undertaken in October by Belgrade "We remain fully vigilant and ready to act," he said.
Serbia's leader, Slobodan Milosevic, may be bargaining that the tough talk will not lead to action at a time when most Western leaders are on holiday and preoccupied with Iraq.Reuse content