Seven people have been injured in clashes between Serbs and ethnic Albanians in the ethnically divided city of Mitrovica in northern Kosovo.
Police from an EU force said they had used tear gas to separate the groups.
In a separate incident in Kosovo's capital, Pristina, police said they had arrested 20 people following a protest against the EU presence there.
Kosovo declared independence from Serbia in February 2008, a move opposed by the Serb minority in the north.
The violence in Mitrovica is said to have started after about 100 Serbs rallied to protest against the re-building of Albanian properties destroyed during the Kosovo conflict in the late 1990s.
Police spokesman Sami Mehmeti said five Albanian construction workers and two Serbs had been injured when stones were thrown.
He said a hand grenade had been detonated and the two groups exchanged small arms fire.
In Pristina, Albanian nationalists overturned or otherwise damaged at least 24 Eulex vehicles, officials said.
The protesters belonged to Self-determination, a group that wants full independence for Albanian-majority Kosovo from Serbia and the international community, AFP news agency reported.
The EU deployed a police, customs and judicial mission after Kosovo declared independence, to replace a UN mission.