Prime Minister Albin Kurti of Kosovo has accused neighbouring Serbia of trying to "provoke a serious international conflict" after two vehicle registration offices near their border were attacked.
The increase in tension early on Saturday occurred on the sixth day of ethnic Serb protests against the ethnic Albanian-led government's decision to require drivers with Serbian registration plates to put on temporary ones when entering Kosovo.
A registration office was torched in the small town of Zubin Potok and another damaged in Zvecan, though there were no casualties, the prime minister said.
Interior Minister Xhelal Svecla wrote on Facebook the blaze that burned down the vehicle registration office in Zubin Potok was done "by suspects in a criminal act with terrorist elements".
Ethnic Kosovo Serbs have blocked the Kosovo-Serbia border with trucks since Monday, angry that Kosovo sent in special police to match Serbia in a number plate move that heightens tensions in the Balkans.
Kosovo now removes number plates from cars entering the country from Serbia, as Serbia does with Kosovo plates. They both force drivers to buy temporary plates.
Serbia does not recognise its former province of Kosovo as a separate nation and considers their mutual border only as a temporary boundary.
Serbia has put its army troops in regions near Kosovo on higher alert. The state RTS television reported on Saturday that Serbian military jets flew in the border area twice during the day, prompting cheers from the protesting Serbs.
On Friday, Serbian army helicopters were also seen flying over the area, Al Jazeera's Boris Gagic reported.
"Individuals and groups, whose activities endanger the rule of law and public order, are attacking our state and disturb our peace," Kurti said on his Facebook account on Saturday.
"Serbia is encouraging them and supports them clearly," he added. "Serbia abuses the citizens of Kosovo in order to provoke a serious international conflict."
Serbian President Aleksandar Vucic has described Kosovo's recent number-plate move as a "criminal action", and he made the withdrawal of all Kosovar special police a condition of European Union-mediated negotiations to resolve the dispute.
But after Saturday's incidents, Kosovo's government did not sound ready to pull the special police back.
"These criminal acts best show what would have occurred with the border crossings in Jarinje and Brnjak unless special forces were sent there to guarantee public order and security," Svecla, the interior minister, wrote on Facebook.
The European Union and the United States have urged Kosovo and Serbia to immediately exercise restraint and refrain from unilateral actions.
Kosovo President Vjosa Osmani called on the world "not to ignore what is clearly (being) seen - a Russian-Serbian tendency to damage the European Union and NATO" by increasing tensions in the Balkans.
"It is time that the international community, and first of all the EU and NATO member countries, see such a danger and prevent the Vucic regime from realizing its goal of creating the 'Serb world,'" she wrote on Facebook, while in New York at the United Nations General Assembly.
A bloody 1998-1999 crackdown by Serbian troops against Kosovo Albanian separatists ended after a NATO intervention, and Kosovo declared independence in 2008.
Thousands of NATO-led peacekeepers, including US troops, are still deployed in Kosovo, trying to stave off lingering ethnic tensions between majority Kosovo Albanians and minority Kosovo Serbs.