A woman wearing leggings with the colours of the US flag walks along a street of Havana on February 18, 2015. President Barack Obama announced Thursday he will make a landmark visit to Cuba on March 21-22, pledging to address human rights as America pursues a historic thaw with its former Cold War foe. (Photo by Yamil Lage/AFP Photo)

People look at a man, who residents said was killed by al Qaeda militants, hanging on a bridge in Yemen's southeastern city of Mukalla June 17, 2015. Al Qaeda militants in Yemen killed two alleged Saudi spies, residents said, accusing them of planting tracking devices which enabled the assassination of the group's leader in a suspected U.S. drone strike. (Photo by Reuters/Stringer)

This file photo provided on Sunday February 15, 2015 by the Syrian anti-government activist group Aleppo Media Center (AMC), which has been authenticated based on its contents and other AP reporting, shows Syrian rebels firing locally made shells against the Syrian government forces, in Aleppo, Syria. (Photo by AP Photo/Aleppo Media Center)

Visitors watch as Grigory Broverman, a member of the Cryophile winter swimmers club, pours a bucket of cold water over his 6-year-old daughter Liza during a flash mob, part of a celebration of Polar Bear Day at the Royev Ruchey Zoo in a suburb of the Siberian city of Krasnoyarsk, Russia, November 29, 2015. The air temperature was around minus 5 degrees Celsius. (Photo by Ilya Naymushin/Reuters)

Robert Galvan, who is on death row for murder, speaks to members of the media at the Adjustment Center yard during a media tour of California's Death Row at San Quentin State Prison in San Quentin, California December 29, 2015. America's most populous state, which has not carried out an execution in a decade, begins 2016 at a pivotal juncture, as legal developments hasten the march toward resuming executions, while opponents seek to end the death penalty at the ballot box. (Photo by Stephen Lam/Reuters)

A woman (L) places flowers at a grave next to a mummified body during exhumation works at the General Cemetery in Guatemala City, April 15, 2015. If a lease on a grave has expired or not been paid, grave cleaners will break open the crypts to remove and rebury the bodies. Any remains that have not been claimed are packed into plastic bags, labeled and stored in mass graves. Bodies that have been stored in the upper crypt are exposed to dry and sunny conditions which means they do not decompose and instead become mummified. (Photo by Jorge Dan Lopez/Reuters)

A woman strikes a police truck with her hand during a protest march in Santiago, Chile, Thursday, April 16, 2015. Thousands of students marched through the streets of Chile's capital to protest recent corruption scandals and to complain about delays in a promised education overhaul. While it was largely peaceful, violence broke out at the end when hooded protesters threw rocks and gasoline bombs at police. (Photo by Luis Hidalgo/AP Photo)

A devotee holds incense sticks while celebrating the Sindoor Jatra Festival on April 15, 2015 in Thimi, Nepal. Sindoor Jatra Festival is celebrated each year in Thimi, on the outskirts of Kathmandu, to welcome the Nepali New Year and celebrate the coming of spring. During the Festival, devotees are smeared with vermillion powder and 30 chariots containing the images of several gods and goddesses are carrying by the devotees around the town, while others sing, dance and play musical instruments. (Photo by Omar Havana/Getty Images)