The trouble started on Saturday morning when Kosovo Albanians assembled for a political rally at a bridge over the Ibar river, which separates the northern town.

When their leaders failed to turn up, the Kosovo Albanians tried to cross the river, but were confronted by the Serbs on the other side of the bridge, some chanting provocative slogans.

The BBC's Orla Guerin reports: "Some in the two polarised communities were spoiling for a fight"

The heavily-armed French peacekeepers tried to defuse the angry crowd as they hurled stones at each other.

At least four Kosovo Albanians were detained, and some handcuffed to lampposts by the French troops. Some of the protestors were injured, though none seriously.

The French Nato commander in the town, Brigadier General Bruno Kush, told the BBC it would have been dangerous to let the Albanians pass.

"Our first priority is to save lives. If we had allowed them through, some might have been lost," he said.

The Albanian protestors dispersed, but insisted they would be back.

Nato had been hoping both sides would eventually sign an agreement on freedom of movement in the town, but a French Nato spokesman admitted there was now little chance of a deal.

Growing concerns

A number of arrests were made as troops fought to restore order

Correspondents say the latest unrest coincides with growing concern over the safety of peacekeeping troops.

Mitrovica has been considered one of Kosovo's major flashpoints because of its large population of Serbs and Kosovo Albanians.

Most of the town's shops and factories as well as the university and hospital are located on the Serbian side of the river.

Many Kosovo Albanians say they were evicted from their homes on the Serb side during the war and both the Serbs and the French peacekeepers have prevented them from returning.

An armed international civilian police is due to begin patrols of the province this weekend in an effort to curb a growing number of inter-communal attacks, primarily by Kosovo Albanians seeking revenge on Serbs.

Raid on KLA house

Elsewhere, Nato peacekeeping troops confiscated illegal weapons and identity cards from the house of a prominent official in the Kosovo Liberation Army.

The official, Rexhep Selimi, is the interior minister in the KLA's unrecognised provisional government.

He was in the house with three other men, but they were not arrested. The KLA has promised to disarm and cease its military activities progressively.

Mr Selimi had been briefly detained by Nato troops on Wednesday for failing to show proper identity papers while in uniform.

Among other items seized at his home were 20 radio frequency scanners and a large quantity of German marks.

Serb backlash continues

In Serbia, the Yugoslav authorities have kept up their attacks on opposition parties, taking the lead from President Slobodan Milosevic's speech on Friday.

Officials and state media described anti-government demonstrators as enemies of the state, intent on introducing a puppet government controlled by the West.

However, opposition rallies continued, with at least 2,000 people protesting in the northwestern town of Vrbas.