Syrian refugees covered with dust arrive at the Trabeel border, after crossing into Jordanian territory with their families, near the northeastern Jordanian border with Syria, and Iraq, near the town of Ruwaished, east of Amman September 10, 2015. (Photo by Muhammad Hamed/Reuters)

Children react after what activists said was shelling by forces loyal to Syria's President Bashar al-Assad near the Syrian Arab Red Crescent center in the Douma neighborhood of Damascus May 6, 2015. (Photo by Bassam Khabieh/Reuters)

The Syrian refugee folklore troupe Abu Rustom perform at a wedding show at Zaatari refugee camp in the Jordanian city of Mafraq, near the border with Syria February 20, 2017. The Syrian troupe is trying to keep its country's traditions alive by holding traditional dances and performing celebratory sword fights during weddings and other occasions, according to the troupe's leader. (Photo by Muhammad Hamed/Reuters)

A man carries a blood stained stretcher in a site hit by what activists said were airstrikes carried out by the Russian air force in the town of Douma, eastern Ghouta in Damascus, Syria January 10, 2016. (Photo by Bassam Khabieh/Reuters)

Students pose for a picture with a 3- D optical illusion artwork of a devastated cityscape in Aleppo, Syria at the campus of the Meiji University in Tokyo on November 18, 2016. The Japanese branch of the human rights organisation Amnesty International displayed the artwork to encourage people to think about the Syrian civil war. (Photo by Toshifumi Kitamura/AFP Photo)

Women, who are members of Saaed group, prepare food to be given out as Iftar meals for the poor and internally displaced Syrians during the month of Ramadan in Damascus, Syria June 18, 2016. Iftar (or Fatoor) is the evening meal when Muslims end their daily Ramadan fast at sunset. Muslims break their fast at the time of the call to prayer for the evening prayer. (Photo by Omar Sanadiki/Reuters)

In this photo taken on Wednesday, February 17, 2016, a volunteer fighter with the Syrian Government forces sits atop a tank in the province of Raqqa, Syria. In recent weeks, Syrian government forces captured dozens of villages and towns across the country. (Photo by Alexander Kots/Komsomolskaya Pravda via AP Photo)

People carry drinks at 80s Bar in Damascus, Syria, March 11, 2016. In Damascus's Old City, just a mile from the battered frontline between government and rebel-held territory, young Syrians smoke, drink beer or soft drinks, and talk about anything but the war. The revival of activity in this once-vibrant quarter is part of efforts to project an air of normality in the Syrian capital, even as the five-year-old war that has killed more than 250,000 people and created 5 million refugees continues to rage nearby. (Photo by Omar Sanadiki/Reuters)