A Syrian man rides his bicycle past a man selling grains during a halt in fighting on February 29, 2016 in Douma, in the Eastern Ghouta region, east of the capital Damascus. A UN-backed ceasefire deal took hold across parts of Syria, bringing relative calm to areas where the Islamic State group and Al-Qaeda's local affiliate are not present. (Photo by Sameer Al-Doumy/AFP Photo)

A man carries an injured girl after what activists said were five air strikes by forces loyal to Syria's President Bashar al-Assad in Douma, eastern al-Ghouta, near Damascus September 11, 2014. (Photo by Bassam Khabieh/Reuters)

Boys pose with their toy guns as others play on swings, on the first day of the Muslim holiday of Eid al-Fitr, which marks the end of the holy month of Ramadan, in the government-controlled district of Dwelaa in Damascus, Syria July 6, 2016. (Photo by Omar Sanadiki/Reuters)

An internally displaced girl stands on an abandoned railway tracks beside a makeshift refugee camp in Sinjar town, in Idlib province, Syria November 20, 2015. (Photo by Ammar Abdullah/Reuters)

Damaged buildings stand in the rebel-controlled area of Maaret al-Numan in Idlib province, Syria September 6, 2016. (Photo by Ammar Abdullah/Reuters)

A Free Syrian Army fighter walks past a flag of al-Furqan brigade as a rifle hangs from a branch in the orchards of Kafar Zita in Hama countryside January 22, 2015. (Photo by Mohamad Bayoush/Reuters)

A clothing shop displays its merchandise in the rebel-controlled city of Idlib, Syria November 7, 2015. (Photo by Ammar Abdullah/Reuters)

In this January 31, 2014 file photo released by the United Nations Relief and Works Agency for Palestine Refugees in the Near East (UNRWA), shows residents of the besieged Palestinian camp of Yarmouk, queuing to receive food supplies, in Damascus, Syria. That year, the U.N. was able to deliver food to about five percent of people in besieged areas including Yarmouk, while today estimates show the organization is reaching less than one percent. (Photo by UNRWA via AP Photo)