Dozens of NATO peacekeepers were injured after they were attacked by ethnic Serbs in northern Kosovo, during protests over the installation of ethnically Albanian mayors.
Violence broke out after Serbian demonstrators tried to block the newly elected mayors from taking office in the northern town of Zvecan on Monday, following a disputed election in April.
While this sort of violence against peacekeepers is rare, tensions have spiked in the region in recent months, fueled by deep historical rifts.
Here's what you need to know.
What's the background?
Kosovo declared independence from Serbia in 2008, following the 1998-99 war in which Kosovar Albanians attempted to break from what was then the Federal Republic of Yugoslavia, made up of today's Serbia and Montenegro. NATO intervened in the war to protect Kosovo's Albanian majority.
Serbia views Kosovo as a breakaway state and does not recognize its independence. Kosovo's Serbs view themselves as part of Serbia, and see Belgrade as their capital, rather than Pristina.
The majority of Kosovo's Serbs -- less than a tenth of the overall population -- live in the northern regions, and have increasingly demanded greater autonomy from the ethnic Albanian majority.
The EU-brokered 2013 Brussels Agreement attempted to normalize relations between the two countries. Under this deal, Serbia could create autonomous municipalities in the northern region, but these would have to operate under the Kosovar legal system, with Kosovar police remaining the only police force.
More than a decade on, these municipalities have not been created, leaving disputes over the degree of autonomy for Kosovo's Serbs to fester.
Even seemingly small details can cause huge flare-ups. For years, Kosovo has wanted Serbs to switch their Serbian car license plates to ones issued by Pristina. Last year, Kosovo's government announced a two-month window in which plates had to be changed -- but pushed the date back after protests.
Ethnic Serb mayors in northern municipalities, along with local judges and some 600 police officers, resigned in November in protest against the looming switch, according to Reuters.
What caused the fresh violence?
In March, the two countries signed a fresh deal in Ohrin, North Macedonia, aiming again to normalize ties. But this was followed by controversial local elections in four municipalities of northern Kosovo.
Serbian President Aleksandar Vucic called on ethnic Serbs in the region to boycott the elections, saying that they should no longer tolerate a foreign "occupation."
Serbian List, the main political party in the region, called on the Serb community not to vote in the elections and on its candidates not to stand -- leaving ethnically Albanian candidates to run unchallenged.
Fearing potential violence, Kosovo's central election commission changed plans to put voting booths in local schools, instead setting up mobile huts patrolled by NATO peacekeepers.
Kosovo's Prime Minister Albin Kurti said there had been a "threatening campaign orchestrated by Belgrade and executed through intimidation, pressure and blackmail by criminal groups."
After polls closed, election officials said only around 1,567 had voted across the four municipalities -- a turnout of 3.5%, according to local media.
The diminished turnout was a mark of the boycott's success in these majority Serb regions. The Zvecan municipality has a population of around 16,800. Of these, more than 16,000 are ethnic Serbs -- with only around 500 ethnic Albanians.
The newly-elected Albanian mayor in Zvecan won with scarcely over 100 votes, prompting cries that his authority is illegitimate.
What happened Monday?
Ethnic Serb protesters threw Molotov cocktails at NATO's Kosovo Force (KFOR) troops and used batons to beat their riot shields, as the peacekeepers defended the municipal office in Zvecan.
KFOR said 30 of its peacekeepers -- mostly from its Italian and Hungarian contingents -- were wounded.
The soldiers suffered from "fractures and burns from improvised explosive incendiary devices," while three soldiers were "wounded by the use of firearms," according to KFOR.
The peacekeeping mission said that it had increased its presence in northern Kosovo after the newly elected ethnically Albanian mayors took office in majority Kosovo Serb areas. Its aim was to "reduce the risk of escalation," KFOR said, but troops were "subsequently attacked by increasingly aggressive crowds."
Kurti condemned the "outrageous attacks" on the peacekeepers. "In a democracy there is no place for fascist violence -- not appeal from ballot to bullet," he tweeted Monday.
In a statement, Serbian Prime Minister Ana Brnabic said the situation in northern Kosovo has "never been more difficult."
What has the reaction been?
European leaders were quick to condemn the violence. Josep Borrell, the European Union's foreign policy chief, said he has had contact with both Kurti and Vučić and asked "both parties to urgently take measures to de-escalate tensions immediately and unconditionally."
Speaking at a press conference in Brussels on Tuesday, Borrell said that the EU "condemns in the strongest terms the violence in the north of Kosovo that we have seen in the last few days."
France's foreign ministry issued a statement claiming "It is more essential than ever for Pristina and for Belgrade to show responsibility by returning to the negotiating table with an attitude of compromise in the service of peace and the prosperity of the Serbian and Kosovar citizens."
While European leaders attempt to strike a careful balance between the two countries, other countries have come to Serbia's defense.
China's ministry of foreign affairs spokesperson Mao Ning said Tuesday: "We support Serbia's effort to safeguard sovereignty and territorial integrity," and called on Pristina to establish Serb majority municipalities.
What happens next?
NATO is deploying additional forces to Kosovo following Monday's clashes, according to a statement on Tuesday.
The violence in Kosovo comes at a precarious political moment in Belgrade. Serbia was rocked earlier this month after two mass shootings killed dozens of people, mostly children.
But what started as candlelit vigils for those killed swelled into fully fledged protests against Vucic's government and the "culture of violence" over which it has prevailed.
"I never, ever saw (Vucic) so nervous," said Boško Jakšić, a foreign policy analyst at the Belgrade Security Forum. "His crisis management is not functioning."
However, the crisis in Kosovo may provide Vucic, who has often used Serbian nationalism as a rallying cry for his supporters, with some welcome relief.
While the streets of Belgrade have recently been flooded with those protesting Serbia's "culture of violence," nationalist demonstrators took to the streets on Tuesday to protest outside the French and German embassies, as Vucic's supporters turned their anger towards the European promoters of Kosovo's independence.
In comments on Tuesday, Vucic stoked fears that the violence in Kosovo may pose a threat to ethnic Serbs in the region, saying Serbia has "concern for the survival and security of Serbs in Kosovo."
"Kosovo is helping him," said Jakšić. "He's building his patriotic stature on Kosovo. He's a big defender of the Serbian cause. He's the savior of the Serbian people... All that rhetoric that we've heard a number of times before is being used again. And there are a lot of people who are buying it."
