Riot police officers in position to crack down on demonstrators during a protest against Venezuelan President Nicolas Maduro, in Caracas on April 20, 2017. Venezuelan riot police fired tear gas Thursday at groups of protesters seeking to oust President Nicolas Maduro, who have vowed new mass marches after a day of deadly unrest. Police in western Caracas broke up scores of opposition protesters trying to join a larger march, though there was no immediate repeat of Wednesday's violent clashes, which left three people dead. (Photo by Juan Barreto/AFP Photo)

A witch doctor prepares an offering for the inauguration of the World People's Conference on Climate Change and the Defense of Life, prior to the World Climate Change Conference, in Tiquipaya, Bolivia, October 10, 2015. Almost 150 nations, including major emitters led by China and the United States, have submitted plans to the United Nations for curbing greenhouse gas emissions blamed by the U.N. for causing more floods, droughts and heat waves. France will host the conference in Le Bourget, near Paris, from November 30 to December 11, 2015. (Photo by David Mercado/Reuters)

Riot police arrest an anti-government protester in Ouagadougou, capital of Burkina Faso, October 30, 2014. Thousands of protesters marched on Burkina Faso's presidential palace after burning the parliament building and ransacking state television offices on Thursday, forcing President Blaise Compaore to scrap a plan to extend his 27-year rule. Emergency services said at least three protesters were shot dead and several others wounded by security forces when the crowd tried to storm the home of Compaore's brother. Security forces also fired live rounds and tear gas at protesters near the presidency in the Ouaga 2000 neighborhood. (Photo by Joe Penney/Reuters)

A girl who suffers from hearing and speech disorders reacts to the camera at a rehabilitation centre supported by Bhopal Medical Appeal, for children who were born with mental and physical disabilities, in Bhopal November 11, 2014. The rehabilitation centre only treats families they believe have been affected by the Union Carbide gas leak 30 years ago. Human rights groups say that thousands of tonnes of hazardous waste remain buried underground, and the government has conceded it is contaminated. There has, however, been no long-term epidemiological research which conclusively proves that birth defects are directly related to the drinking of the contaminated water. (Photo by Danish Siddiqui/Reuters)

Serbian police officers of the Special Anti-Terrorist Unit pose for a picture in their base outside Belgrade October 8, 2014. When the killing of an unarmed black teenager by a white policeman in Ferguson, Missouri, in August sparked sometimes violent protests, the response of police in camouflage gear and armoured vehicles wielding stun grenades and assault rifles seemed more like a combat operation than a public order measure. Some U.S. police departments have recently acquired U.S. military-surplus hardware from wars abroad, but there are many law enforcers around the world whose rules of engagement also allow the use of lethal force with relatively few restrictions. But for every regulation that gives police wide scope to use firearms, there is another code that sharply limits their use. In Serbia, police may use measures ranging from batons to special vehicles, water cannon and tear gas on groups of people who have gathered illegally and are behaving in a way that is violent or could cause violence, but they may use firearms only when life is endangered. (Photo by Marko Djurica/Reuters)

A man sits next to a damaged idol of Hindu goddess Kali which was taken out after its immersion in the river Ganges in Haridwar, India, March 29, 2017. (Photo by Danish Siddiqui/Reuters)

An Orthodox activist (Right) clashes with a gay rights campaigner during a protest outside of the State Duma, Russian Parliament's lower chamber, in downtown Moscow, January 22, 2013. (Photo by Ilya Pitalev/RIA Novosti)