Serbian Prime Minister Aleksandr Vucic has been chased from a Srebrenica memorial ceremony by an angry crowd throwing stones and bottles.
The incident happened as thousands of people gathered in the Bosnian town to remember the 1995 massacre of 8,000 Muslim men and boys by Bosnian-Serb troops.
Bodyguards whisked Vucic through angry mourners as the crowd surged up a hill behind his delegation. They ran for their cars, with a Bosnian government source saying the delegation had now left the site.
The killing was the bloodiest massacre in Europe since the Second World War, but many Serbian nationalists still refuse to call it genocide.
The Serbian government has in the past apologised for the massacre, but recently Mr Vucic asked Russia to veto a UN security council motion calling Srebrenica a “crime of genocide”.
The men accused of being the chief architects of the massacre, Radovan Karadzic and Ratko Mladic, are currently on trial for war crimes in the Hague.