Kosovo must grant greater autonomy to Serb-majority municipalities in the country’s north if it is to come closer to joining NATO and the European Union, according to the US ambassador to the Western Balkans on Wednesday.

Violence has erupted after Kosovo authorities installed ethnic Albanian mayors in municipal offices after they were elected on a turnout of only 3.5%, infuriating Serbs who form a majority in northern districts and had boycotted local elections.

Gebriel Escobar also urged Kosovo to withdraw police and mayors from their offices in Serb-majority areas to de-escalate tensions and then hold fresh municipal elections in which Serbs would participate.

“If Kosovo wants to move towards Euro-Atlantic integration it will have to establish (an association of Serb municipalities),” Escobar told reporters in the U.S. embassy in Belgrade.

“So it will happen. The question is, will it happen with this (Kosovo) government or a next, a future government.”

Serbia, which backs around 50,000 Serbs in northern Kosovo both financially and politically, would have to ensure that the region’s Serbs took part in the new election, Escobar added.

Four predominantly Serb municipalities in northern Kosovo see Belgrade as their capital and are defying the government in Pristina.

The Serbs in north Kosovo left the country’s institutions last December. They want greater autonomy, under the provisions of a 2013 EU-sponsored agreement which envisaged the formation of an Association of Serb Municipalities.

Prime Minister Albin Kurti is reluctant to implement the accord because he fears that if granted more autonomy, the Serbs could hold a referendum to join Serbia instead of staying as part of Kosovo.

Reinforcements for NATO’s peacekeeping force began to arrive in Kosovo this week following the recent unrest.

Kosovo declared internationally recognised independence from Serbia in 2008, nearly a decade after NATO bombing drove the Serbian army and police from the teritory. Serbia still regards Kosovo as its southern province.