Kosovo Prime Minister Hashim Thaci is defending his police attempt to seize two border posts in a Serb area as a step to establish law and order in all of Kosovo.
The police action left one officer dead and another wounded, along with three civilians.
Mr. Thaci said Tuesday that Kosovo cannot remain indifferent while part of its territory remains in what he called a black hole.
Serbian President Boris Tadic said the police action was intended to take over Serb areas and is completely unacceptable. He warned any outsiders who would encourage the Kosovo police that they would be making a terrible mistake and put the Balkans at risk.
Kosovo police forces tried to take over the Brnjak and Jarinje crossings on the Serbian border late Monday. Their action triggered fighting with Serbian protesters. One Kosovo officer died after he was shot in the head. A second officer was wounded by a grenade. Reports say three civilians also were wounded.
NATO says Kosovo police have agreed to pull back from the border area, but it is still not clear who controls the posts.
Serbs living in northern Kosovo refuse to recognize Kosovo's independence and the ethnic Albanian government's authority.
Kosovo also is trying to enforce a recent ban on Serbian exports. Serbia banned goods from Kosovo when it declared independence from Serbia in 2008. Serbs say they will never recognize an independent Kosovo, but want to settle their differences with Kosovo through negotiations.