Serbs attacked a U.N. convoy carrying Serb detainees from a raid in Kosovo on Monday, enabling several detainees to escape, witnesses said.

The attack occurred after U.N. police stormed the main U.N. court in the northern flashpoint town of Mitrovica, retaking it from Serbs who had forcibly occupied the building three days earlier. Dozens of Serbs were arrested in the raid.

U.N. police fired tear gas to try and disperse hundreds of Serbs who gathered after the raid and began clashing with the police and NATO peacekeeping troops.

Serb youths threw stones and firecrackers at French NATO troops and the cabin of one NATO vehicle was seen ablaze.

A Reuters witness said the detainees escaped when the Serbs forced open one vehicle in the U.N. convoy.

The 120,000 Serb minority among two million ethnic Albanians rejects Kosovo's February 17 declaration of independence from Serbia. Belgrade has vowed to never accept the secession and to extend its authority over Serb areas in the territory's north.

More than 500 mainly Ukrainian U.N. police were involved in the dawn raid.

Before the operation hundreds of French troops in armoured vehicles, part of a 16,000-strong NATO peacekeeping force in Kosovo, had blocked access roads to the court compound in the north of the town, which is divided between Serbs and Albanians.

The detained Serbs offered no resistance as they were led handcuffed to U.N. vehicles. Police removed a Serbian flag from the building.