An international commemoration of the Srebrenica massacre was marred as people pelted Serbian Prime Minister Aleksandar Vucic with water bottles, stones and other missiles.
The event was held to mark 20 years since the slaughter of 8,000 Muslims from the town by Bosnian Serb forces.
Foreign Secretary Philip Hammond condemned the actions of a "few individuals" who targeted the Serbian leader.
Mr Vucic was forced to flee for safety as he was pelted with missiles at the event.
Mr Hammond said: "People from across Bosnia and Herzegovina, the region and the international community gathered at Potocari today to commemorate the genocide in Srebrenica and victims on all sides of the conflict in Bosnia and Herzegovina.
"I welcome in particular Serbian Prime Minister Aleksandar Vucic's attendance at the Srebrenica memorial and deplore the way a few individuals have sought to ruin the solemnity of today's commemoration.
"Their action should not be allowed to detract from the sentiments felt by a majority; that the countries and peoples of the western Balkans need to move forward together in reconciliation and co-operation."