Syrians gather during an evacuation operation of rebel fighters and their families from rebel-held neighbourhoods on December 15, 2016 in the embattled city of Aleppo. A convoy of ambulances and buses left rebel territory in Aleppo in the first evacuations under a deal for opposition fighters to leave the city after years of fighting. The rebel withdrawal will pave the way for President Bashar al-Assad's forces to reclaim complete control of Syria's second city, handing the regime its biggest victory in more than five years of civil war. (Photo by Karam Al-Masri/AFP Photo)

People who fled the violence from Islamic State-controlled northern Syrian town of al-Bab arrive in the rebel-held outskirts of the town, Syria February 3, 2017. (Photo by Khalil Ashawi/Reuters)

A Syrian Democratic Forces (SDF) female fighter adjusts a mortar in northern Deir al-Zor province ahead of an offensive against Islamic State militants, Syria February 21, 2017. (Photo by Rodi Said/Reuters)

Eritrean refugee children play at Mai-Aini refugee camp near the Eritrean boarder in the Tigrai region in Ethiopia February 10, 2016. Each month as many as 5,000 people flee Eritrea according to U.N. figures, estimates the Eritrean government disputes. The government puts the population at about 3.6 million, while other estimates suggest it could be almost double that. (Photo by Tiksa Negeri/Reuters)

A fighter belonging to Jaish al-Islam (Islam Army) runs to take cover near the frontline on March 14, 2016 in the neighbourhood of Jobar, on the eastern outskirts of the capital Damascus. (Photo by Amer Almohibany/AFP Photo)

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)

A Russian ground staff member signals to the pilot of a Sukhoi Su-25 fighter jet at the Hmeymim air base near Latakia, Syria, in this handout photograph released by Russia's Defence Ministry October 22, 2015. (Photo by Reuters/Ministry of Defence of the Russian Federation)

Internally displaced Syrian children play inside a refugee camp in the Hama countryside, Syria January 1, 2016. (Photo by Ammar Abdullah/Reuters)