Military vehicles surround a wreckage of a trolleybus, in Volgograd, Russia, Monday, December 30, 2013. A bomb blast tore through a trolleybus in the city of Volgograd on Monday morning, killing at least 10 people a day after a suicide bombing that killed at least 17 at the city's main railway station. Volgograd is about 650 kilometers (400 miles) northeast of Sochi, where the Olympics are to be held. (Photo by Denis Tyrin/AP Photo)

Tourists look at other festival-goers playing in the mud during the Boryeong Mud Festival at Daecheon beach in Boryeong, about 190 km (118 miles) southwest of Seoul, July 19, 2013. About 2 to 3 million domestic and international tourists visit the beach during the annual mud festival, according to the festival organisers. (Photo by Lee Jae-Won/Reuters)

An employee walks near a rotary dredge which works on the coal face of the Borodinsky opencast colliery, near the Siberian town of Borodino, east of Krasnoyarsk, December 9, 2014. The Borodinsky colliery, 9 km (5.6 miles) long and more than 100 meters (328 feet) deep, annually produces more than 20 million tons of coal and is considered to be the biggest opencast coal mine in Russia, according to official representatives. (Photo by Ilya Naymushin/Reuters)

Indian men stand around sword fish for sale at a harbour a harbour in Chennai on June 5, 2016, as fishermen return with their catch after a 45-day fishing ban on the east coast of India. Authorities in the southern Indian state of Tamil Nadu had imposed a 45-day ban on fishing by mechanised vessels to protect marine life, with only “country boats” operating within five nautical miles off the coast. (Photo by Arun Sankar/AFP Photo)

Brave slackliners have been pictured walking the ropes above Rio de Janeiro, Brazil on August 15, 2016, with the half a mile drop showing the city in all its glory. The stunning shots show the daredevils tread across an eighty-two-foot-long high line on Pedra da Gvea mountain with an amazing sunrise illuminating the city landscape behind. (Photo by Rafael Moura/Caters News Agency)

In this March 22, 1975 file photo, a refugee clutches a baby as a government helicopter gunship carries them away near Tuy Hoa, Vietnam, 235 miles northeast of Saigon. They were among thousands fleeing from Communist advances. AP Photographer Nick Ut will be retiring from the AP in March 2017 after 51 years of taking photographs from the front lines of the Vietnam War to the red carpets of Hollywood. (Photo by Nick Ut/AP Photo)

Master Sergey Suprun uses a portable radio set as he stands near a rotary dredge which works on the coal face of the Borodinsky opencast colliery, near the Siberian town of Borodino, east of Krasnoyarsk, Russia October 27, 2015. The Borodinsky colliery, 9 km (5.6 miles) long and more than 100 meters (328 feet) deep, annually produces more than 20 million tons of coal and is considered to be the biggest opencast coal mine in Russia, according to official representatives. (Photo by Ilya Naymushin/Reuters)

A member of Kyrgyzstan's first female hockey team arrives for a training session in the village of Otradnoye, Kyrgyzstan on February 4, 2020. Based in the remote village of Otradnoe, 249 miles (400 kilometres) east of the country's capital Bishkek, the team comprises of around 15 girls from a local school and uses a flooded allotment to train on during the winter months. (Photo by Vladimir Pirogov/Reuters)