Pieter Feith, envoy of the European Union and head of the EU mission in Kosovo, condemned the incident and said he was looking to the UN to restore order.
"I would like to appeal to them, to resist from further violence and to respect the mandate of the United Nations."
Fatmir Sejdiu, Kosovo's president, and Hashim Thaci, the prime minister, demanded that Unmik and Nato peacekeepers should react urgently.
They urged international authorities in Kosovo to "pull the hooligans out of the buildings as well as to provide permanent protection against them".
In February this year, Kosovo's government unilaterally declared independence from Serbia and has since been recognised by many western countries.
Serbia has declared the move as illegal and two days after the declaration angry Kosovo Serbs had torched two border crossings with Serbia.