Serbia's foreign minister, Vuk Jeremic, has formally protested the establishment of an International Steering Group to oversee developments in Kosovo.

In a letter to United Nations Secretary-General Ban Ki-moon, Jeremic called the group "illegal" because it falls outside of the U.N. mandate in Kosovo.

Envoys from 15 nations that recognize Kosovo independence attended Thursday's inaugural session in Vienna of the group that is to guide Kosovo's democratic development.

Meanwhile, Serbian authorities have filed criminal charges against 80 people for their role in last week's violence by opponents of Kosovo independence at the U.S. and other embassies in Belgrade

In another development, hundreds of Kosovo Serb police in various Serb enclaves failed to report for duty Friday. They joined their colleagues in the Gnjilane region who earlier this week began protests against the decision of the area's ethnic Albanians to declare independence.

Late Thursday, an explosion near a police station in the Serb-held part of the divided city of Mitrovica destroyed at least two U.N. vehicles.

Some information for this report was provided by AP.