On Sunday, NATO chief Jens Stoltenberg called on Kosovo to tone down tensions with Serbia, two days after violent clashes between Kosovo police and demonstrators opposed to Albanian mayors taking office in ethnic Serb regions.
Stoltenberg said he had spoken to European Union foreign policy chief Josep Borrell Josep Borrellon Kosovo.
He added that Pristina and Belgrade should engage in a dialogue led by the EU.
"Pristina must de-escalate & not take unilateral, destabilising steps," Stoltenberg wrote on Twitter.
Serbs, who make up the majority of the population in the northern region of Kosovo, do not accept Kosovo's 2008 declaration of independence from Serbia and still see Belgrade as their capital more than two decades after the war ended in 1999.
Ethnic Albanians make up more than 90% of the population in Kosovo as a whole.
Serbs refused to participate in local elections in April, and Albanian candidates won the four municipalities by 3.5%.
The local Serbs, supported by Belgrade, pointed out that they would not accept the mayors and that they did not represent them.
On Friday, three out of four mayors were escorted to their offices by police. The demonstrators threw stones at the authorities, who responded with tear gas and water cannons to disperse the angry crowds.
The situation remained tense on Sunday as heavily armed policemen in armored vehicles still guarded the mayors' offices.
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