A demonstrator shows his bottom to riot police during a protest by European workers and trade union representatives to demand better job protection in the European Union countries in Brussels, in this March 24, 2011 file photo. (Photo by Thierry Roge/Reuters)

A naked protester runs past the parliament in Syntagma Square in Athens during a violent protest against the visit of Germany's Chancellor Angela Merkel, in this October 9, 2012 file photo. (Photo by John Kolesidis/Reuters)

A woman pleads to be released by the police after she was surrounded during an evening demonstration against police violence in Oakland, California, in this December 13, 2014 file photo. (Photo by Stephen Lam/Reuters)

An Egyptian Christian clashes with Egyptian riot police in front of the the Coptic Orthodox church in Alexandria, 230 km (140 miles) north of Cairo, in this January 1, 2011 file photo. (Photo by Amr Abdallah Dalsh/Reuters)

A protester throws a stone at police in front of the Greek Parliament building during clashes in Athens, in this December 12, 2008 file photo. (Photo by John Kolesidis/Reuters)

Nationalist youths and police in riot gear clash in the Ardoyne area of north Belfast, in this July 12, 2011 file photo. (Photo by Cathal McNaughton/Reuters)

A local woman on a crutch shouts at Chinese paramilitary police wearing riot gear as a crowd of angry locals confront security forces on a street in the city of Urumqi in China's Xinjiang Autonomous Region, in this July 7, 2009 file photo. (Photo by David Gray/Reuters)

An anti-establishment protester tries to attack riot police during a protest against high security prisons in Athens, in this April 16, 2015 file photo. (Photo by Alkis Konstantinidis/Reuters)

An opposition supporter gestures in front of riot police guarding the presidential palace in Taipei, in this March 21, 2004 file photo. (Photo by Thomas White/Reuters)

Members of the Palestinian security forces take part in a training session in the West Bank city of Ramallah, in this September 18, 2011 file photo, simulating a scenario of violence ahead of the Palestinians' bid for statehood at the United Nations on Friday. (Photo by Mohamad Torokman/Reuters)

A protester urinates in front of a row of policemen during riots following the death of a 15-year-old boy in San Carlos de Bariloche, in this June 18, 2010 file photo. (Photo by Alejandra Bartoliche/Reuters)

A protester takes cover during clashes with riot police in front of the Interior Ministry in Cairo, in this June 29, 2011 file photo. (Photo by Mohamed Abd El-Ghany/Reuters)

A pro-democracy demonstrator gestures at policemen during a protest organised by the “February 20 Movement”, who are demanding political reforms, in Casablanca, in this May 29, 2011 file photo. (Photo by Reuters/Macao)

A pro-democracy protester stands in front of a line of riot police at Mongkok shopping district in Hong Kong early, in this October 17, 2014 file photo. (Photo by Bobby Yip/Reuters)

A student of the Buenos Aires University Union Federation (FUBA) kicks a barrier in front of the Congress in Buenos Aires, in this December 14, 2009 file photo, amid clashes with riot police during a protest staged to avoid an assembly to elect the new rector of the university. (Photo by Joaquin Salguero/Reuters)

A Beijing citizen stands in front of tanks on the Avenue of Eternal Peace in this June 5, 1989 file photo during the crushing of the Tiananmen Square uprising. (Photo by Arthur Tsang/Reuters)

A protestor faces a line of riot police during an anti-government protest in Budapest, in this October 23, 2006 file photo. (Photo by Laszlo Balogh/Reuters)

A student protester clashes with the police during a rally against the government's plans to increase fuel prices, in front of the presidential palace in Jakarta, in this May 21, 2008 file photo. (Photo by Dadang Tri/Reuters)

An indigenous woman holds her child while trying to resist the advance of Amazonas state policemen who were expelling the woman and some 200 other members of the Landless Movement from a privately-owned tract of land on the outskirts of Manaus, in the heart of the Brazilian Amazon, in this March 11, 2008 file photo. (Photo by Luiz Vasconcelos-A Critica/Reuters/AE)