What is Behind the Rising Tensions Between Kosovo and Serbia?

Dozens of NATO peacekeepers were injured this week in northern Kosovo when they clashed with ethnic Serbs, raising fears of a larger escalation between Serbia and Kosovo.

The violence came after Kosovo’s ethnic Albanian leadership sent heavily armed security forces to take control of town municipal buildings, the latest turn in a dispute that has roots going back to the Balkan conflicts of the 1990s.

Kosovo, where a majority of the population is ethnic Albanian and Muslim, declared its independence from Serbia in 2008, almost a decade after NATO’s bombing campaign that drove Serb forces, responsible for years of brutal mistreatment of ethnic Albanians, from Kosovo.

Since then, the two countries have clashed over Kosovo’s treatment of its minority ethnic Serb population.

The fighting in recent days — mostly skirmishes, but also some shooting — began when the Kosovan government deployed its security forces in several towns to install the ethnic Albanian mayors who had won in local elections last month. Local Serbs had mostly boycotted those votes.

Each side has blamed the other for the fighting. NATO’s secretary general, Jens Stoltenberg, called the recent clashes “unacceptable” on Tuesday and said that 700 reserve troops had been deployed to help the peacekeeping mission there, which included 3,800 troops before the conflict. In response to the violence, Serbia’s president, Aleksandar Vucic, said in a statement released by his office that he had put the army on the highest level alert.

Here is what we know.

How did the violence start?

The recent clashes were centered on four northern municipalities bordering Serbia that are home to much of Kosovo’s Serb minority.

Serbian nationalists living in Kosovo, many of whom still regard the Serbian capital, Belgrade, as their true capital, have staged protests throughout the past decade to resist integrating with Kosovo.

The boycott of local elections last month was prompted by a Serbian political party in Kosovo. In a statement posted to Facebook days before the election, the group dismissed the process as “undemocratic” and urged Serbs to stay home on voting day.

“Serbs should watch with contempt all those who go out to participate in this illegal and illegitimate process that is against the interest of the Serbian people,” the post said.

To ensure that the ethnic Albanians who won recent mayoral elections could take their posts, Kosovo’s central government last week sent in armed security forces to the area, a move that was condemned in unusually strong terms by the United States, Kosovo’s main international backer. Secretary of State Antony J. Blinken on Friday accused Kosovo’s ethnic Albanian leadership of “escalating tensions in the north and increasing instability.”

Over the weekend, Serb protesters gathered outside municipal buildings in a number of Serbian-majority towns, facing off with Kosovo security forces and troops from a NATO-led peacekeeping mission called KFOR.

A total of 30 NATO peacekeepers, including 19 Italians and 11 Hungarians, suffered injuries in the clashes. More than 50 Serbs were treated for injuries, Mr. Vucic said.

The NATO mission’s commander, Maj. Gen. Angelo Michele Ristuccia, in a statement urged both sides to “take full responsibility for what happened and prevent any further escalation.”

Tensions in the region had been building since the elections last month.

In a televised statement early Tuesday, Mr. Vucic blamed Kosovo’s prime minister, Albin Kurti, for fueling hostilities. He also criticized NATO’s peacekeeping mission, saying it had failed to protect the Serbian population and was enabling the “illegal and forceful takeover” of the majority-Serbian municipalities by the Kosovan government.

Mr. Kurti, Kosovo’s prime minister, applauded the NATO forces, saying they had been trying to curb the “violent extremism” in the streets. “In a democracy there is no place for fascist violence,” he said in a statement on Twitter. “Citizens of all ethnicities have a right to full & unencumbered service of their elected officials,” he added.

What’s behind the conflict?

The latest escalation is part of a dispute over the status of Kosovo, which declared its independence 15 years ago, almost a decade after NATO’s 78-day bombing campaign in 1999 that drove Serb forces, then engaged in brutal mistreatment of ethnic Albanians, from Kosovo.

While an independent Kosovo has been recognized by the United States and many European countries, Serbia — as well as its key allies, Russia and China — still refuses to recognize Kosovo’s independence. It has called the split a violation of U.N. resolution 1244 that dates back to 1999 and the end of the Kosovo war.

President Vucic and other Serbian leaders claim Kosovo as being the “heart” of their country, in part, because it houses many revered Orthodox Christian sites. Mr. Vucic has ruled out recognizing Kosovo and vowed to “protect” ethnic Serbs.

Serbian nationalists in Kosovo have been joined by more moderate Serbs in demanding the implementation of a 2013 deal brokered by the European Union that calls for a measure of self-rule for Serb-dominated municipalities in the north, a provision Kosovo has reneged on.

In February, leaders of Kosovo and Serbia tentatively accepted a peace deal, which was mediated by the European Union and rejected by nationalists on both sides. It has not been formally signed.

What is the regional backdrop to the tensions?

Tensions between the two ethnic communities have flared regularly over the past decade, making the region a hub of unpredictable violence.

Clashes erupted last July in response to a new law that would require ethnic Serbs living in Kosovo to switch from Serbian license plates to Kosovar ones.

The recent escalation of hostilities comes as Russia’s invasion of Ukraine has absorbed the attention of Kosovo’s important allies, the United States and the European Union.

Serbia, a candidate to join the European Union, has been a close partner with Moscow for centuries. While it voted in favor of a U.N. resolution condemning the Russian invasion of Ukraine, Serbia has refused to join sanctions imposed on Moscow by Western countries.

“Serbs are fighting for their rights in northern Kosovo,” Foreign Minister Sergey V. Lavrov of Russia said on Monday during a visit to Kenya. “A big explosion is looming in the heart of Europe,” he said.

Joe Orovic and Andrew Higgins contributed reporting.