Tensions are rising in the north of Kosovo as Pristina's mainly ethnic Albanian rulers try to assert control over a slice of the north mainly populated by ethnic Serbs.
Kosovo Prime Minister Hashim Thaci told RFE/RL's Balkan Service his government wants to install police and customs officers at two border posts in the north.
Serbian President Boris Tadic warned at a news conference in Belgrade that such a move could spark tensions.
"Any deployment of representatives of the so-called Kosovo customs, Kosovo's security forces, or so-called border service to administrative crossings would represent an instant violation of the neutral status of these institutions ( KFOR and EULEX), a violation of all international decisions and decisions of the Security Council," he said.
Serbian Foreign Minister Vuk Jeremic has lodged a protest with UN Secretary-General Ban Ki-moon.
As night fell, Serbs in the north halted a convoy of German NATO soldiers heading north to the border.
Serbs in the divided town of Mitrovica set up barricades of buses, rocks and lorries loaded with stones.
with agency reports