A police officer gives instructions to migrants rushing to board a train that would take them towards Serbia, at the railway station in the southern Macedonian town of Gevgelija, Wednesday, August 20, 2015. Macedonian police stepped up the security at the border with Greece apparently trying to stem recent surge of migrants who are coming from Greece. (Photo by Darko Vojinovic/AP Photo)

Riot police fire tear gas at demonstrators during a protest against fare hikes for city buses in Sao Paulo, Brazil, January 8, 2016. Brazilian riot police on Friday fired tear gas and stun grenades to disperse a violent protest against a rise in public transport fares in the country's largest city, Sao Paulo. (Photo by Nacho Doce/Reuters)

Residents observe a police officer take up position during an operation at the Mare slums complex in Rio de Janeiro March 25, 2014. The federal troops have taken control of security operations in Mare slums complex to help quell a surge in violent crime following attacks by drug traffickers on police posts in three slums on the north side of the city, government officials said. (Photo by Ricardo Moraes/Reuters)

Romanian riot police detain a man, face covered in blood, after minor clashes erupted during a protest in Bucharest, Romania, Thursday, February 2, 2017. Brief clashes broke out between protesters and police in Romania¹s capital, as tens of thousands of people protested for the second night a government decision to decriminalise official misconduct. (Photo by Vadim Ghirda/AP Photo)

A demonstrator is carried away by plain-clothes police during a march against government reforms and cost-cutting measures in Brussels , October 7, 2015. (Photo by Francois Lenoir/Reuters)

A Macedonian police officer hits a stranded migrant attempting to cross the Greek-Macedonian border, near Gevgelija, Macedonia December 2, 2015. Picture taken from the Greek side of the border. (Photo by Alexandros Avramidis/Reuters)

Police officers standby while a forest fire burns the hills of Valparaiso city, northwest of Santiago, March 13, 2015. Several hectares of land has been burned due to forest fires near Valparaiso city, with no report of deaths or injuries, local authorities said. (Photo by Lucas Galvez/Reuters)

A protester reacts as police use water cannon during a demonstration to demand changes in the Chilean education system in Santiago, Chile June 25, 2015. (Photo by Ueslei Marcelino/Reuters)