By the BBC's Nick Wood in Pristina

The Polish Prime Minister, Leszek Miller, is travelling to Kosovo on Tuesday to visit 15 Polish police officers injured in serious clashes in the province.

Sixteen men, serving with the United Nations riot unit, were wounded in the fighting in the divided city of Mitrovica on Monday, one of them seriously.

The UN's presence is opposed by many Serbs

The Polish officers, serving with the UN riot unit, had been deployed to the Serbian-dominated north of the city.

They were backing up a group of police officers who came under attack when they began checking drivers documents.

In the ensuing clashes, groups of Serb men threw grenades at the riot police and fired with automatic weapons.

UN struggle

UN police officers responded with tear gas and gunfire.

Most of the injured policemen suffered shrapnel wounds, and one is due to be airlifted to Poland for further treatment.

Following the clashes, the police were withdrawn from patrolling in the north of the city and retreated to a UN compound.

Many of the local Serb population are strongly opposed to the UN's presence in the region.

As well as visiting injured officers, Mr Miller is expected to hold talks on the current situation in Mitrovica with the head of the UN mission in Kosovo, Michael Steiner.

He will be accompanied by Poland's interior minister and the head of the police force.

It is almost three years since the UN took over the administration of the Yugoslav province and control of Mitrovica.

But still, the mission is struggling to complete operations that might be described as routine police work in other countries.

The latest violence has raised further questions about its ability to maintain law and order.