Western officials have accused the Serbian government of stirring up ethnic tensions in the divided Kosovan town of Mitrovica.

On Monday, Nato-led peacekeeping troops used tear gas to disperse thousands of Kosovo Albanian protesters trying to cross a bridge linking the Serb to the Albanian sides of the town.

The American ambassador to the United Nations, Richard Holbrooke squarely blamed Belgrade for the recent violence.

And Nato Secretary-General George Robertson warned Belgrade that the organisation would not tolerate fresh conflict after monitoring a build-up troops close to Serbia's border with Kosovo.

Troops massing

Mr Robertson issued a strong warning to that the alliance would not allow a fresh outbreak of conflict.

"There is certainly rising tension in he southern part of Serbia and large numbers of additional Yugoslav troops have moved into the area," Mr Robertson said.

"There is no doubt that Milosevic will have a hand in some of the provocations on the Serb side. A robust response, as usual, is the best way to deal with Milosevic," he added.

Ambassador Holbrooke emphatically blamed Yugoslavia's leaders for the violence in Mitrovica.

"I think there is no question who's responsible for it. It's Belgrade. The leadership in Belgrade is fomenting trouble north of the Mitrovica bridge".

Mr Holbrooke described it as "absolutely appalling" that people in Kosovo were throwing stones and endangering the lives of Nato peacekeepers.

Quiet returns

A BBC correspondent in the region reports that quiet has returned to Mitrovica and the streets are deserted.

Earlier, K-For troops had struggled to contain a protest by thousands of local people that was swelled by 30,000 marchers from Pristina.

The demonstrators broke through a cordon of largely British soldiers and attempted to storm the heavily-guarded bridge between the Serb north and Albanian south that has frequently been a flashpoint for violence.

Following a tense stand-off, K-For troops fired tear gas and drove the demonstrators back.

Meanwhile, thousands of Serbs on the other side of the bridge played loud nationalist music to taunt the Kosovo Albanians.

An upsurge of clashes in Mitrovica - one of the last remaining towns in Kosovo with a substantial Serb population - has left nine people dead in recent weeks.

For several months, Kosovo Albanians have been prevented from reaching the Serb side of town, including the hospital and the university, while Serbs have been unable to go to the post office on the southern side.