Ukraine's President Petro Poroshenko (L) and U.S. Vice President Joe Biden pose for the media prior to meeting on the sidelines of the World Economic Forum in Davos, Switzerland, January 20, 2016. REUTERS/Michel Euler/Pool

Congolese civilians walk past a house and vehicles which were burnt during anti-government protests to press President Joseph Kabila to step down in the Democratic Republic of Congo's capital Kinshasa, September 21, 2016. REUTERS/Kenny Katombe

Venezuela's President Nicolas Maduro speaks during his weekly broadcast "En contacto con Maduro" (In contact with Maduro) in Caracas, Venezuela September 20, 2016. Miraflores Palace/Handout via REUTERS

FILE PHOTO -- Cast member Marion Cotillard poses on the red carpet as they arrive for the screening of the film "Juste la fin du monde" (It s Only the End of the World) in competition at the 69th Cannes Film Festival in Cannes, France, May 19, 2016. REUTERS/Regis Duvignau/File Photo

FILE PHOTO - Labourers work on piles of sugarcanes at a sugar refinery in Menghai county, Yunnan province December 6, 2011. REUTERS/Wong Campion

An Inyo County Search and Rescue helicopter searches Bear Creek Spire, in the Sierra National Forest, California, U.S. in this September 21, 2016 handout photo for the body of Maria Birukova, a medical student at Stanford University who was killed after plunging down a steep slope while climbing. Inyo County Search and Rescue/Handout via Reuters

A labourer works at a cold-rolling mill of the Wuhan Iron & Steel Group on the outskirts of Wuhan, capital of central China's Hubei province August 22, 2006. REUTERS/Alfred Cheng Jin/File Photo

U.S. Vice President Joe Biden gestures during a news conference at the Swedish government offices, Rosenbad in Stockholm, Sweden, August 25, 2016. REUTERS/Anders Wiklund/TT News Agency