(CNN) -- A demonstration along the Kosovo-Serbian border turned violent Wednesday when ethnic Serbs set fire to a customs building, and attacked NATO and EU police, authorities said.
The ethnic Serbs, upset over a Kosovo government-ordered post along the border, used petrol bombs to set fire to the building, and threw rocks and debris at personnel, a NATO officer said.
"The situation is now under control, but tense," said Lt. Col. Ralf Adametz, a NATO operation officer.
Security forces did not report any serious injuries.