Three UN cars were damaged in an explosion in a residential area of the Kosovo capital Pristina today, but no one was hurt, witnesses said.
"We are checking what happened," a police spokesman said.
A police source said it appeared an explosive device had been placed under one of the cars.
Tensions are rising in Serbia's UN-run province as a decision nears on the 90 per cent Albanian majority's demand for independence.
Serbs and Albanians are due to meet on Wednesday in Vienna for final talks on a UN plan unveiled this month which would, if adopted by the UN Security Council, set the province on the path to statehood.
But some Albanians are angry at provisions for a powerful European overseer and broad self-government for the 100,000 Serbs, which they say will only prolong Kosovo's limbo status.
Two protesters died during clashes on February 10 between police and ethnic Albanians demonstrating against the plan, the worst violence since March 2004. Kosovo Prime Minister Agim Ceku said police had used excessive force and the head of the UN police force resigned.
Kosovo has been run by the United Nations since 1999, when NATO bombs drove out Serb forces accused of killing and expelling civilians in a two-year counter-insurgency war.
Western powers support the plan drafted by former Finnish president Martti Ahtisaari, but have twice delayed the process in the past three months to avoid radicalising Serbia.