Government offices in Kosovo were attacked on Saturday as tensions with Serbia over a row over vehicle license plates escalate.
Serbia doesn't recognise its former province's nation status and forces drivers from Kosovo to buy temporary plates when entering the country.
Now Kosovo has decided to do the same.
In response, ethnic Serbs in Kosovo blocked the provisional border with trucks, and two government offices in the capital Pristina have been attacked.
"The incineration of the vehicle registration center in Zubin Potok last night after midnight was no accidental fire, but a deliberate fire," said Albin Kurti, Kosovo Prime Minister, "and in the vehicle registration center in Zvecan, two hand grenades were thrown out of the window, which fortunately did not explode. Investigations will shed light on both cases."
The Kosovo Serbs say they will keep up their blockade at the crossing until Pristina withdraws its decision to replace Serbian license plates with Kosovo ones.
Serbia has placed army units near Kosovo on high alert and state media reported that military jets have been flying near the border.
Serbian President Aleksandar Vucic has described Kosovo's recent license 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.
The European Union and the United States have urged Kosovo and Serbia to exercise restraint and refrain from unilateral actions.
A bloody 1998-1999 crackdown by Serbian troops against Kosovo Albanian separatists ended after NATO intervention, and Kosovo declared independence in 2008. It has been recognized by the US and other Western nations, but not by Serbia and allies Russia and China