Ethnic tensions are rising in Kosovo, setting the stage for an early test of U.S.-Russian relations under President Donald Trump in a Balkan country where U.S. troops keep the peace decades after a NATO air campaign ended Serb rule over the Albanian population.

A 78-day U.S.-led bombing campaign in 1999 forced Serbia to give up control of Kosovo, which Serbs consider their historic homeland, after months of reprisal killings and forced dislocations by armed Serbs and ethnic Albanian rebels.