Serbia's state-run Tanjug news agency said several armed U.N. guards and about 30 Kosovo Police Service guards didn't engage the mob and offered no resistance.

The Serbs broke through a cordon into the Municipal and District Court in Kosovska Mitrovica and went to the roof, where they replaced the U.N. flag with the Serbian flag, the report said.

Serbs in the town have been having protest rallies around the courthouse since Feb. 21, four days after Kosovo declared independence from Serbia. Many of the protesters are former employees of the court who were dismissed when U.N. forces took over regional administration in 1999, the report said.

Kosovo has about 2 million ethnic Albanians, while there are some 120,000 Serbs, who maintain Kosovo is the birthplace of Serbia.