Military law imposed on divided Kosovo town after Serb rioting

Nato has put the northern Kosovo town of Mitrovica under de facto military law after rioting by Serbs hostile to the newly independent state left one UN policeman dead and forced the withdrawal of UN staff.

The violence, which erupted on Monday at the UN courthouse in the divided town, was the worst since Kosovo's Albanian majority declared independence from Serbia last month. Nato officials said that protesters had "crossed a red line", using Molotov cocktails and grenades. A 25-year-old Ukrainian policeman died after being caught in by a grenade blast, becoming the first UN policeman to die in Kosovo since the UN took control in 1999.

In Mitrovica, the main bridge over the river that separates the town's Serb north from the Albanian south, was closed. French, Belgian and Spanish peacekeepers from the Nato-led force in armoured personnel carriers secured potential flashpoints and a column of US troops arrived to provide back-up. Meanwhile, all Kosovo Serb police officers were ordered to suspend normal duties.

Larry Rossin, the second-in-command of the UN mission in Kosovo, accused Serbia's authorities of being behind the violence. "It is clear to us that the violence ... was orchestrated," he said. "We've never had what we could consider a clear and unambiguous denunciation of this kind of violence from the ministers or indeed any other Belgrade government official that I can think of."

The unrest will have strengthened the hand of ultranationalists in Serbia, which vehemently rejected Kosovo's secession, ahead of parliamentary elections on 19 May. Some 120,000 Serbs live in the north and scattered in enclaves in the south of Kosovo. Policemen, doctors and teachers in the area still follow orders and take salaries from the Serbian government.

There have been reports, carried in Zeri, Kosovo's biggest-selling daily, that Serbia has offered to formally govern ethnic Serb areas in Kosovo. The proposal, believed to have been made at the weekend by Serbia's Minister for Kosovo, Slobodan Samardzic, would in effective partition Europe's newest country and is said to have been rejected by the UN mission in Kosovo (UNMIK). Mr Rossin said that he had met Mr Samardzic and was given a document meant to be "a framework for a comprehensive relationship between Serbia and UNMIK", but would not comment on its contents.

The International Crisis Group, the Brussels-based think-tank, said in a report that the UN, Nato and the EU had been caught unprepared by Serb tactics and needed to co-ordinate better. "Serbia and Russia need to receive some very clear messages that partition of Kosovo is unacceptable", said Sabine Freizer, director of its Europe programme.

Monday's rioting was triggered by a UN police operation to remove Serbian protesters from a UN courthouse that they had been occupying for almost four days. In addition to the death of the policeman, another 42 officers and 22 peacekeepers were injured.

Yesterday, charred vehicles and burnt-out rubbish littered streets close to the courthouse. French peacekeepers fired warning shots into the air to disperse a group of stone-throwing protesters, but no one was hurt.