People gather at the site of a bomb explosion in Sanaa December 23, 2014. Five bombs exploded on Tuesday in Sanaa's old quarter, where many supporters of the Shi'ite Muslim Houthi group live, killing at least one person and wounding another, a Yemeni security official said. No one has claimed responsibility for the attacks, but the Houthis have been fighting the Sunni Islamist militant al Qaeda group and allied tribesmen since its gunmen captured Sanaa in September and forced the resignation of a government they had long seen as corrupt. (Photo by Khaled Abdullah/Reuters)

Roped up climbers leave the summit of Breithorn at 4,164 metres (13,661 feet) on the ridge marking the border with Switzerland (left) and Italy in the Alpine resort of Zermatt August 4, 2014. Switzerland will vote on November 30 on an initiative from the group Ecopop which proposes a cap on the number of immigrants. The group says it is motivated by concerns about a lack of living space exerting too much pressure on the land and natural resources, rather than by opposition to foreigners. (Photo by Denis Balibouse/Reuters)

A ballet dancer attends a photo shooting as activists from the environmentalist group Greenpeace unfurl a giant banner on the Eiffel Tower which reads “Liberty, Equality, Fraternity” in a call on French citizens to vote against the National Front (FN) presidential candidate Marine Le Pen, in Paris, France May 5, 2017. (Photo by Gonzalo Fuentes/Reuters)

A Libyan fireman stands in front of smoke and flames rising from an oil storage tank at an oil facility in northern Libya's Ras Lanouf region on January 23, 2016, after it was set ablaze earlier in the week following attacks launched by Islamic State (IS) group jihadists to seize key port terminals. (Photo by AFP Photo/Stringer)

The Tsaatan people are one of the world’s last groups of nomadic reindeer herders and they live in Khövsgöl Aimag in northern Mongolia. They are originally from across the border in what is now the Tuva republic of Russia. (Photo by Pascal Mannaerts/Rex Feature/Shutterstock)

A group of people are seen on a Victoria line train in London, England during the first night of the Night Tube service on August 19 2016. The Central line and Victoria line are the first to operate a Night service with further lines expected to be running by the end of the year. (Photo by SWNS.com)

Activists and supporters of Ukrainian nationalist groups light flares during a rally to mark the third anniversary of the Euromaidan Revolution in downtown Kiev, Ukraine, 21 November 2016. About one thousand activists took park in the rally during which they burned tires on the Independence Square, destroyed the Russian bank Sberbank and broke windows in the office of a Ukrainian politician Viktor Medvedchuk, according to Ukrainian media. (Photo by Roman Pilipey/EPA)

The singing group The D-Day Darlings take part in the unveiling ceremony of a permanent war memorial, created by artist and writer Fabian Peake, at St Pancras International railway station in London, Britain, November 8, 2018. (Photo by Peter Nicholls/Reuters)