BRUSSELS (Reuters) – NATO Secretary-General Jens Stoltenberg called on Kosovo to ease tensions with Serbia on Sunday, two days after clashes between Kosovo police and protesters opposed to Albanian mayors taking office in ethnic Serb regions.

Stoltenberg, the Norwegian secretary-general of the transatlantic military alliance, said he had spoken to EU foreign policy chief Josep Borrell about Kosovo and that Pristina and Belgrade should engage in EU-led dialogue.

“Pristina must de-escalate and not take destabilizing unilateral steps,” Stoltenberg said in a tweet.

Serbs, who make up the majority of the population in Kosovo’s northern region, do not accept the 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, said 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, who threw stones and responded with tear gas and water cannons to disperse protesters.

Heavily armed policemen in armored vehicles were still guarding the mayors’ offices on Sunday.

A joint statement from the embassies of the United States, Italy, France, Germany and Britain known as the Quint Group and the EU office in Pristina Kosovo warned against any further measures to enforce access to municipal buildings.

“We strongly warn all parties against threats or other actions that could affect a safe and secure environment, including freedom of movement, which could lead to heightened tensions or spark conflict,” the EU said.

“The new unilateral measures will negatively affect relations with the five countries and the European Union.”

The United States, Britain and the European Union are the main backers of Kosovo as the country remains a non-member of the United Nations due to objections from Serbia, Russia, China and others.

(Reporting by Sabine Siebold), additional reporting by Fatos Baetsi in Pristina, written by Fu Yun-chi; Editing by Sharon Singleton and Alexander Smith

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