By the BBC's Nick Wood In northern Mitrovica

After one of the most violent clashes in northern Mitrovica for over a year there is not a single UN policeman to be seen on the streets, the local Serb population has erected barricades and young men with walkie-talkies stand at crossroads.

A few metres away French soldiers serving with the Nato-led peacekeeping force, K-For, look on dispassionately.

It all shows that little has changed in Mitrovica since the UN first took on the administration of the province in June 1999.

Groups of men known colloquially as the "bridge watchers" have effectively policed the Serb-dominated north of the city at the expense of the UN's own police force.

"Rather than confront these groups, the United Nations has allowed them to grow outside the office of the UN," says Robert Curris, regional representative of the charity, the European Centre for Minority Issues. He was speaking after 16 UN police officers were injured in Monday's clashes.

"What we saw in Mitrovica was a direct result of the UN's and K-For's failure to live up to its mandate and keep the north of the city under control."

UN officers attacked

Since 1999, the UN's police officers have come under repeated attack by the self-styled security groups.

According to the UN's regional police commander, this latest violence was a direct result of the attempt to crack down on their activities.

Most of the policemen injured on Monday were Poles

"They are trying to regain the ground they have lost. We are becoming more effective," says John Neil, a police officer seconded to Kosovo by the Police Service of Northern Ireland.

He says most of the Serb population want to see the return of ordinary policing, and that they are being intimidated by a criminal minority who are intent on keeping control of the area.

Operations that may be taken for granted in most other countries, such as routine vehicle checks, have only just started in the last few months in the Serb-dominated north of the city.

Yet as the result of one these operations, 16 police officers were injured. Patrolling in the north was suspended and the UN began to evacuate police personnel from their homes for fear they could be attacked.

"It's difficult because we are not able to defend ourselves here," said one Slovenian officer, based in the Mitrovica north police station.

"We do have the help of special police units, but the problem is that they can take 10, 20, 30 minutes to come, and a lot can happen in that time".

Call for bigger force

Many in the local police station believe they do not have sufficient officers or equipment to be able to patrol the area effectively.

There are currently 65 officers from more than 30 countries such as Canada, Britain, Jordan, Ghana, the Philippines and Nigeria. One senior officer said it would take between 90 to 100 properly trained policemen to control the area properly.

The regional commander says their numbers will soon be increased.

They also say they are handicapped by the lack of armoured vehicles, meaning that police patrols are suspended as soon as there is violence on the streets.

K-For accused

K-For undoubtedly has the numbers and capability to deal with such situations. However, UN police officers still accuse of them of failing to act when needed.

I've seen fellow officers under attack and the French are standing there not 20 yards away doing nothing

US officer in Mitrovica

On Monday, a platoon of Polish riot police was prevented from crossing to the north of the city after French soldiers received orders to close the bridge that links it with the Albanian dominated south.

They eventually found an alternative route. A misunderstanding perhaps, but some officers says this reflects an overall trend.

One US officer from Texas, who has been in Mitrovica for five months, says: "I've seen fellow officers under attack and the French are standing there not 20 yards away, doing nothing."

The complaint echoes that of another Texan UN officer just over two years ago. Former station commander JD Luckie was transferred from Mitrovica in February 2000 after he made similar complaints about the French peacekeeping troops.

Improved relations

Regional commander John Neil says relations between K-For and UN police have improved.

He says only last weekend, French troops backed the police as they came under attack from a mob, but more still needs to be done.

"It's a bad situation - in the middle of a riot they have access to grenades and AK47s." He says K-For is ultimately responsible for ensuring that there are no armed groups in the centre of one of Kosovo's largest cities. "K-For still have tactical primacy. It's a long-inherited problem."

Robert Curris says it is not simply a question of law and order. He says clashes in Mitrovica have a ripple effect on the rest of Kosovo.

"At this point, the UN and K-For's failure to live up to their mandate and establish security in the north of Mitrovica is affecting communities throughout Kosovo, and polarising the different ethnic groups, particularly Serb and Albanian."