Masked youths set fire to one of two border posts on Kosovo's northern frontier on Wednesday. Nato forces said they had been fired upon at the posts, which have been at the centre of rising tension this week.
RTS national television showed footage of young masked people, apparently ethnic Serbs, throwing Molotov cocktails at the Jarinje border post and destroying it with the help of a bulldozer.
About 25 police and border officers, including some from the European Union's Eulex mission, took refuge on the Serbian side of the border, according to witnesses.
Eulex said no one was injured in the attack.
Nato's Kfor mission in Kosovo said in a statement that its personnel near the border post had been fired upon, and said it was reinforcing its presence in the area to prevent further incidents.
Kosovo's Prime Minister Hashim Thaci accused “the highest political structures of the government of Serbia" of being behind the attack.
EU foreign affairs chief Catherine Ashton also condemned violence in the area.
On Monday, the ethnic-Albanian-dominated government in Pristina sent elite police units to seize control of the Brnjak and Jarinje border crossings. One officer was killed and four others hurt in a clash with angry local Serbs.
The officers were withdrawn on Wednesday, officials said.
The goal of the operation was to replace local Serb police officers accused of turning a blind eye to imports from Serbia after a ban was introduced a week ago.