Serbian President Aleksandar Vucic placed the country's army on full combat alert and ordered its units to move closer to the border with Kosovo, the Tanjug news agency reported on Friday.
Vucic's orders came as Serbs in the northern Kosovo's municipality of Zvecan clashed with Kosovo police who were trying to help the newly elected ethnic Albanian mayor enter his office.
The local vote had been boycotted by Serbs who represent a majority in the area.
Local media reported that Kosovo police fired tear gas at a crowd gathered in front of the municipality building.