Soviet Army soldiers sit on their tanks in front of the Czechoslovak Radio station building in central Prague during the first day of Soviet-led invasion to then Czechoslovakia on August 21, 1968. (Photo by Libor Hajsky/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)

Two Czech Gripen fighter planes demonstrate a flight interception of a Belgian air force transport plane over the Czech Republic, as part of NATO drills on September 12, 2018. (Photo by Francois Lenoir/Reuters)

Women walk past a mannequin with a covered face as they shop ahead of the Muslim festival of Eid-al-Adha in Aleppo, Syria September 23, 2015. (Photo by Hamid Khatib/Reuters)

Przemek Pawlicki performs during training in Leszno, Poland on May 12, 2016. A stunning action-packed catalogue of photographs from sporting events around the world has been released by Red Bull. The energy drink giant's photographers have been busy capturing extraordinary images of action sports and some of the world's greatest daredevils. (Photo by Lukasz Nazdraczew/Red Bull/SWNS.com)

Anna Malova, Miss Russia 1998, poses on a pool table at The Campbell Apartment restaurant in Grand Central Station on November 18, 1999. She makes her motion picture debut in the movie “Above Ground”. (Photo by Richard Corkery/NY Daily News Archive via Getty Images)

In this combination image visitors to the London Super Comic Convention dress as their favourite Marvel comic characters at ExCel on February 25, 2012 in London, England. Visitors to the Comic Convention are encouraged to wear a costume of their favourite character. (Photo by Peter Macdiarmid/Getty Images)

Nyibol Lual, 13 years old, helps her family to prepare the land for cultivation on May 31, 2017, in Panthau, Northern Bahr al Ghazal, South Sudan. The family has a small land where they cultivate sorghum. An estimated 63 per cent of the population in Northern Bahr al Ghazal is experiencing severe food insecurity, according to the latest Integrated Food Security Phase Classification (IPC) report. The situation is particularly bad in Aweil West and Aweil South counties, where the exhaustion of household food stocks and growing dependence on financially inaccessible markets have left the population facing Emergency levels of food insecurity. (Photo by Albert Gonzalez Farran/AFP Photo)