Bodyguards use umbrella to protect Serbia's Prime Minister Aleksandar Vucic during unrest at a ceremony marking the 20th anniversary of the Srebrenica massacre in Potocari, near Srebrenica, Bosnia and Herzegovina July 11, 2015. Serbian Prime Minister Aleksandar Vucic was chased out of a ceremony marking the 20th anniversary of the Srebrenica massacre on Saturday by a crowd throwing stones and bottles. It was not clear whether Vucic had left the site altogether, but his delegation was seen running for their cars on a hill above the cemetery. REUTERS/Antonio Bronic TPX IMAGES OF THE DAY 

Bodyguards protect Serbia's Prime Minister Aleksandar Vucic (3rd L with spectacles) during unrest at a ceremony marking the 20th anniversary of the Srebrenica massacre in Potocari, near Srebrenica, Bosnia and Herzegovina, July 11, 2015. Serbian Prime Minister Aleksandar Vucic was chased out of a ceremony marking the 20th anniversary of the Srebrenica massacre on Saturday by a crowd throwing stones and bottles. It was not clear whether Vucic had left the site altogether, but his delegation was seen running for their cars on a hill above the cemetery. REUTERS/Sanel Mumic TPX IMAGES OF THE DAY

A stone is thrown at Serbia's Prime Minister Aleksandar Vucic as bodyguards use umbrella to protect him during unrest at a ceremony marking the 20th anniversary of the Srebrenica massacre in Potocari, near Srebrenica, Bosnia and Herzegovina July 11, 2015. Serbian Prime Minister Aleksandar Vucic was chased out of a ceremony marking the 20th anniversary of the Srebrenica massacre on Saturday by a crowd throwing stones and bottles. It was not clear whether Vucic had left the site altogether, but his delegation was seen running for their cars on a hill above the cemetery. REUTERS/Stoyan Nenov TPX IMAGES OF THE DAY 

Bodyguards protect Serbia's Prime Minister Aleksandar Vucic during unrest at a ceremony marking the 20th anniversary of the Srebrenica massacre in Potocari, near Srebrenica, Bosnia and Herzegovina, July 11, 2015. Serbia's prime minister Vucic was forced to flee a ceremony held to mark 20 years since the Srebrenica massacre on Saturday, when mourners hurled stones and bottles at him in what his government later described as an attempted assassination. REUTERS/Sanel Mumic 

A man who disturbed security during a ceremony marking the 20th anniversary of the Srebrenica massacre, is carried away by security officers in Potocari, near Srebrenica, Bosnia and Herzegovina July 11, 2015. Abandoned by their U.N. protectors toward the end of a 1992-95 war, 8,000 Muslim men and boys were executed by Bosnian Serb forces over five July days, their bodies dumped in pits then dug up months later and scattered in smaller graves in a systematic effort to conceal the crime. REUTERS/Antonio Bronic 

A protester is held by a policeman during unrest at a ceremony marking the 20th anniversary of the Srebrenica massacre in Potocari, near Srebrenica, Bosnia and Herzegovina July 11, 2015. Serbian Prime Minister Aleksandar Vucic was chased out of a ceremony marking the 20th anniversary of the Srebrenica massacre on Saturday by a crowd throwing stones and bottles. It was not clear whether Vucic had left the site altogether, but his delegation was seen running for their cars on a hill above the cemetery. REUTERS/Stoyan Nenov 

A banner reading 'For one Serbian we are going to kill 100 muslims!', a quote attributed to Serbian Prime Minister Aleksandar Vucic, is seen during a burial ceremony in Potocari, near Srebrenica, Bosnia and Herzegovina July 11, 2015. The bodies of the 136 recently identified victims of Srebrenica massacre are buried in Potocari during ceremonies to mark the 20th anniversary of the massacre. Abandoned by their U.N. protectors toward the end of a 1992-95 war, 8,000 Muslim men and boys were executed by Bosnian Serb forces over five July days, their bodies dumped in pits then dug up months later and scattered in smaller graves in a systematic effort to conceal the crime. More than 1,000 victims have yet to be found. REUTERS/Antonio Bronic 

Police detain a protester during unrest at a ceremony marking the 20th anniversary of the Srebrenica massacre in Potocari, near Srebrenica, Bosnia and Herzegovina July 11, 2015. Serbian Prime Minister Aleksandar Vucic was chased out of a ceremony marking the 20th anniversary of the Srebrenica massacre on Saturday by a crowd throwing stones and bottles. It was not clear whether Vucic had left the site altogether, but his delegation was seen running for their cars on a hill above the cemetery. REUTERS/Stoyan Nenov 

Serbian Prime Minister Aleksandar Vucic observes a moment of silence during a ceremony marking the 20th anniversary of the Srebrenica massacre in Potocari, near Srebrenica, Bosnia and Herzegovina July 11, 2015. Abandoned by their U.N. protectors toward the end of a 1992-95 war, 8,000 Muslim men and boys were executed by Bosnian Serb forces over five July days, their bodies dumped in pits then dug up months later and scattered in smaller graves in a systematic effort to conceal the crime. REUTERS/Antonio Bronic TPX IMAGES OF THE DAY 

Serbia's Prime Minister Aleksandar Vucic lays flowers during a ceremony marking the 20th anniversary of the Srebrenica massacre in Potocari, near Srebrenica, Bosnia and Herzegovina July 11, 2015. Abandoned by their U.N. protectors toward the end of a 1992-95 war, 8,000 Muslim men and boys were executed by Bosnian Serb forces over five July days, their bodies dumped in pits then dug up months later and scattered in smaller graves in a systematic effort to conceal the crime. REUTERS/Antonio Bronic

Serbia's Prime Minister Aleksandar Vucic sits alone before the speeches during a ceremony marking the 20th anniversary of the Srebrenica massacre in Potocari, near Srebrenica, Bosnia and Herzegovina July 11, 2015. Abandoned by their U.N. protectors toward the end of a 1992-95 war, 8,000 Muslim men and boys were executed by Bosnian Serb forces over five July days, their bodies dumped in pits then dug up months later and scattered in smaller graves in a systematic effort to conceal the crime. REUTERS/Dado Ruvic