Iraqi pro-government forces fire an anti-tank cannon near al-Sejar village, north-east of Fallujah, on May 25, 2016, as they take part in a major assault to retake the city from the Islamic State (IS) group. Iraqi forces, consisting of special forces, soldiers, police, paramilitary-fighters and pro-government tribesmen, launched a major assault to retake Fallujah, the scene of deadly battles during the US occupation and one of the toughest targets yet in Baghdad's war on the Islamic State group. (Photo by Ahmad Al-Rubaye/AFP Photo)

A 10-year-old boy living on the streets of New Delhi lies down on cascading water of a fountain in the gardens of the India Gate monument on May 20, 2016. The Indian Meteorological Department issued warnings of “severe heat wave” conditions across large parts of India's north and west, including the capital Delhi, where temperatures hit 47 degrees Celsius. (Photo by Roberto Schmidt/AFP Photo)

Colorado Gov. John Hickenlooper shows off his socks--one with Democratic presidential candidate Bernie Sanders and the other with Republican candidate Donald Trump – before entering his former brewpub for a book signing event to mark the release of his autobiography Thursday, May 26, 2016, in Denver. Hickenlooper, who is term-limited, is doing book talk rounds this week, reviving speculation that he is positioning himself to join Hillary Clinton's presidential campaign ticket. (Photo by David Zalubowski/AP Photo)

A worker at the Jabal Saraj cement factory poses for a photograph in Jabal Saraj, north of Kabul, Afghanistan April 19, 2016. In an area desperately short of industry and jobs, local workers hope that the relaunch of the plant in Jabal Saraj, built by Czech engineers in 1957 and closed down by the Taliban in 1995, can show that Afghanistan's shattered industry can climb back to its feet after decades of war and destruction. But the outdated state-owned plant some 75 kilometres outside Kabul also shows how far it has to go before that promise can be achieved and there are serious questions over whether it has a viable future unless a new, modern facility is built to replace it. (Photo by Ahmad Masood/Reuters)

Chicken, fish and eggs lie next to coca paste worth $14,000 Colombian pesos at a local store in Guyabero Region, Guaviare, Colombia, May 24, 2016. As the government nears a historic peace deal with the rebels of the Revolutionary Armed Forces of Colombia (FARC), the nation's authorities are struggling to tame an increase in farming of coca, the raw material used to make cocaine. In the Guyabero Region, where many people work on coca plantations, locals barter coca paste to buy groceries at the local shop. (Photo by John Vizcaino/Reuters)

A student aims a stick of wood at Bolivarian National Police officers during clashes outside the Central University in Caracas, Venezuela, Thursday, June 9, 2016. Students had planned to march from Venezuela's top university to elections headquarters, but hundreds of police in riot gear blocked the way. Students covered their faces with Venezuelan flags and threw bottles, stones and sticks while police lobbed tear gas. (Photo by Fernando Llano/AP Photo)

People walk along the Dune du Pilat (Dune of Pilat), the tallest sand dune in Europe, in La Teste de Buch, near Bordeaux, France, June 15, 2016. The dune has a volume of about 60,000,000 m³, measuring around 500 m wide from east to west and 2.7 km in length from north to south. Its height is currently 110 meters above sea level. (Photo by Sergio Perez/Reuters)

European Space Agency astronaut Tim Peake will return home after a six-month long mission on the International Space Station,on June 18, 2016. Peake was the first British ESA astronaut to visit the ISS and captured hundreds of photographs of the Earth during his mission. Here: “Lots of sun-glint right now during our whole orbit – we haven't seen a sunset for over 3 days”, he wrote. (Photo by Tim Peake/ESA/NASA)