A mob of angry ethnic Serbs threw firebombs and set fire to a security post on Kosovo's northern border with Serbia, hours after Kosovar special police withdrew from the area.
There were no immediate reports of injuries in the incident, which took place at the Jarinje border crossing.
Kosovar Prime Minister Hashim Thaci accused official Belgrade in connection with the attack. He said "a criminalized group, led by leaders of Serb parallel structures and motivated by the authorities in Belgrade, has attacked Border Checkpoint No. 1 in the north."
Serbian President Boris Tadic swiftly issued a statement demanding the immediate end to the use of violence at the Jarinje checkpoint, and called on ethnic Serbian citizens in Kosovo to remain calm.
"I sharply condemn the violence," Tadic said. "Extremists and hooligans, with their violent moves work against interests of citizens and the state of Serbia and thus join the extremists on the Albanian side, who by unilateral acts and violence want to end the peaceful process of dialogue between Pristina and Belgrade."
KFOR, NATO's Kosovo force, issued a statement saying that there were also confirmed reports of shots fired at KFOR personnel in the vicinity of the Jarinje border post.
KFOR said it was reinforcing security there "in order to prevent further escalation of the situation."
The attack comes as Kosovar police said an operation to take control of two disputed border posts
in the Serb-run north had ended.
Police spokesman Brahim Sadriu said earlier that control over the border crossings in the Serb-dominated northern part of Kosovo was handed over to border police and customs officers.
The move by special police forces on the night of July 25-26 met with resistance from local Serbs and resulted in the death of one police officer.
The European Union and the United States criticized Kosovo's ethnic Albanian majority leadership for not coordinating their action with the international community.
The order to take control of the border crossings on July 25 came after Kosovo last week imposed a ban on goods from Serbia, in response to Serbia refusing to lift a similar ban it imposed on goods from Kosovo after Kosovo declared independence in 2008.
Serbia rejects Kosovo's independence, saying the territory is still part of Serbia.
Earlier, Serbia's Tadic
described the Kosovar actions as "unacceptable," but said Serbia would not attempt to use force to resolve the matter.
with reporting by RFE/RL's Kosovo subunit and news agencies