The most senior UN official in Kosovo has said he has ordered the police to retake the courthouse, and pledged to defend his mandate as head of UN mission known as Unmik.

'Red lines'

"Those who turned to violence in North Mitrovica have crossed one of Unmik's red lines. This is completely unacceptable," Joachim Ruecker said.

"I have instructed Unmik police to restore law and order in the north and to ensure that the courthouse is again under UN control."

He said the attackers would be prosecuted and called upon Serbian authorities to prevent any further such incidents.

Many of the protestors had lost their jobs when the UN took over local institutions at the end of the war in Kosovo in 1999.

The Serbs have held daily protests in front of the court since Kosovo declared independence from Serbia on February 17.

The crowds have prevented international and ethnic Albanian judges from returning to work at the court.

Protesters' views

Miodrag Ralic, one of the Serb protest leaders, said: "We tried to negotiate, but no one wanted to talk to us. We could not wait any longer."

Nebojsa Jovic, another protest leader, said: "We have nothing against international judges. We want to co-operate with all non-Albanians and all those who do not recognise independent Kosovo."

Scheffer, left, met Sejdiu, centre, and
Thaci in Pristina, Kosovo's capital [EPA]
A spokesman for Kosovo's police in Kosovska Mitrovica said that the regional UN representative was negotiating with Serb leaders to deal with the situation.

Meanwhile, Jaap de Hoop Scheffer, Nato's secretary-general, arrived for his first visit to Kosovo since it declared independence last month.

Scheffer met Hashim Thaci, Kosovo's prime minister, and Fatmir Sejdiu, the country's president, at Nato's headquarters in the capital, Pristina.

Sejdiu said he has urged Nato and the UN authorities to "react urgently and oust the hooligans from the building" and restore the UN flag.

The storming of the courthouse appeared to have been co-ordinated with the Serbian government in Belgrade, which has rejected Kosovo's declared statehood and said it will assume authority in northern Kosovo.

Belgrade 'Action Plan'

Belgrade has adopted an "Action Plan" on Kosovo, which took effect after Kosovo declared independence.

Although concrete measures proposed in the plan remain secret, some of them were leaked by the local media, and included the takeover of the judiciary in the Serb-controlled regions of Kosovo.

During earlier protests outside the court, UN and local staff were forced to leave after Serb rioters threw hand grenades at the building.

Since the declaration of independence, Kosovo Serbs have tried to take control of a stretch of rail line in northern Kosovo in defiance of Kosovo's government.

Hundreds of Serb policemen have handed over their badges and weapons rather than submit to Kosovo authorities.