Approximately two dozen NATO peacekeepers were injured by Serb protesters in northern Kosovo on Monday—escalating tensions that’s put Serbia’s army on “the highest level of combat alert,” Reuters reports. The Kosovo Force, the NATO-backed security outfit tasked with maintaining order in the region, said in a statement they were attacked “unprovoked” and “sustained trauma wounds” from incendiary devices hurled by protesters. The alleged attack reportedly injured 20 Hungarian soldiers—seven seriously—and others from Italy. Serbia President Aleksandar Vucic said 52 Serbs were injured in the clashes, which took place outside city halls near Kosovo’s border with Serbia. Monday’s violence is the latest to rock northern Kosovo, which has been a regular hotbed of protest and riots by Serbs who still reject the country’s 2008 declaration of independence from Serbia and its rule by ethnic Albanians, which make up 90 percent of the population.