A picture released by the North Korean Central News Agency (KCNA) shows Kim Jong-un convening an urgent operation meeting at 0:30 am on March 29, 2013 at an undisclosed location, in which he ordered strategic rocket forces to be on standby to strike US and South Korean targets at any time. (Photo by KCNA via EPA)

Chinese military medics take part in a parade commemorating the 70th anniversary of Japan's surrender during World War II held in front of Tiananmen Gate in Beijing, Thursday, September 3, 2015. (Photo by Ng Han Guan/AP Photo)

An Iraqi soldier stands guard as a pipeline burns in the background after an explosion 30 kilometers (20 miles) northeast of Tikrit, Iraq, Monday, February 11, 2008. (Photo by Bassem Daham/AP Photo)

A U.S. Marine leads training on a shooting range in France in an undated photo taken during the First World War. (Photo by Reuters/Courtesy Library of Congress)

A walruses at Hagenbeck Zoo in Hamburg, Germany on July, 7, 2015. (Photo by Werner Struss/Startraks action)

A chimpanzee looks in the direction of a camera at the Gut Aiderbichl Sanctuary for Traumatized Chimpanzees and other Primates in Gaenserndorf, near Vienna, 17 September 2018. 34 former laboratory chimpanzees of former Austrian pharmaceutical company Immuno AG spend their lives at the Gut Aiderbichl Sanctuary for Traumatized Chimpanzees and other Primates since 2009. (Photo by Christian Bruna/EPA/EFE)

An Exmoor wild goat silhouetted in the sky over the Bristol Channel at the valley of the Rocks, North Devon, as the UK's heat wave continues on July 19, 2018. (Photo by Paul Silver/South West News Service)

An aircraft passes over houses at it lands at Heathrow Airport near London, Britain, December 11, 2015. Picture taken December 11, 2015. (Photo by Neil Hall/Reuters)