Civilians wait to be bussed out of besieged areas of eastern Aleppo, Syria, as evacuations continue on Monday, December 19. A people-swap deal struck between rebels and Syrian government forces was set to begin over the weekend, but evacuations were temporarily put on hold after a number of buses were set on fire. Mamun Ebu Ömer/Anadolu Agency/Getty Images
Syrian pro-government forces wave to evacuees from the villages of Foua and Kefraya on December 19. While people were being bused out of Aleppo, safe passage was also given to people in areas held or besieged by rebels, the Aleppo Media Center activist group said. GEORGE OURFALIAN/AFP/Getty Images
Militants burned at least five buses assigned to evacuate people in Aleppo on Sunday, December 18. Aleppo has been held by rebels for the past four years, but it is now almost entirely under government control. SANA/AP
Buses drive through the Syrian government-controlled crossing of Ramoussa, on the southern outskirts of Aleppo, on December 18. GEORGE OURFALIAN/AFP/Getty Images
Russian soldiers and Syrian pro-government forces look on as civilians and rebel fighters are evacuated from Aleppo on Friday, December 16. Evacuations began a day earlier under a new ceasefire between rebels and pro-government forces. STRINGER/AFP/Getty Images
Pro-government forces guard a convoy of buses and ambulances during the evacuation operation on December 16. GEORGE OURFALIAN/AFP/Getty Images
Civilians arrive in the opposition-controlled Khan al-Aassal region, to the west of Aleppo, on Thursday, December 15. Most of the civilians from Aleppo will be taken to a rebel-controlled area in the neighboring province of Idlib. BARAA AL-HALABI/AFP/Getty Images
A wounded boy sits inside an ambulance during the evacuations on December 15. KARAM AL-MASRI/AFP/Getty Images
Staff members of the Syrian Red Crescent wait near ambulances as the evacuation operation gets underway on December 15. KARAM AL-MASRI/AFP/Getty Images
Buses line up to transport people away from eastern Aleppo on December 15. Aleppo Media Center/Facebook
A woman leads family members toward the evacuation buses on December 15. KARAM AL-MASRI/AFP/Getty Images
A woman in a wheelchair waits to board a bus during evacuations on December 15. KARAM AL-MASRI/AFP/Getty Images
A member of the civil defense carries a wounded boy out of a hospital in eastern Aleppo on December 15. Yahya Alrejjo /Anadolu Agency/Getty Images
Pro-government forces advance in Aleppo on Wednesday, December 14. GEORGE OURFALIAN/AFP/Getty Images
A wounded woman is helped into the bed of a truck on December 14. GEORGE OURFALIAN/AFP/Getty Images
Buses wait to evacuate people in Aleppo on December 14. GEORGE OURFALIAN/AFP/Getty Images
Pro-government forces advance on December 14. GEORGE OURFALIAN/AFP/Getty Images
Pro-government forces walk in the ancient Umayyad Mosque after capturing the area on Tuesday, December 13. GEORGE OURFALIAN/AFP/Getty Images
Syrians depart a rebel-controlled area of Aleppo on December 13. KARAM AL-MASRI/AFP/Getty Images
Syrian residents, fleeing violence in the Bustan al-Qasr neighborhood, arrive in Aleppo's Fardos neighborhood on December 13. STRINGER/AFP/Getty Images
A Syrian child cooks in the street in a rebel-held area of Aleppo on December 13. STRINGER/AFP/Getty Images
Syrian civilians take food from a storage room that was formerly held by the opposition forces in eastern Aleppo's al-Kalasseh neighborhood on December 13. STRINGER/AFP/Getty Images
Pro-government fighters wave from a truck as they pass civilians fleeing the Bustan al-Qasr neighborhood on December 13. STRINGER/AFP/Getty Images
A woman reacts as she evacuates the Bustan al-Qasr neighborhood with her two children on December 13. STRINGER/AFP/Getty Images
Syrians celebrate in a government-held district of Aleppo on Monday, December 12. STRINGER/AFP/Getty Images
Pro-government forces patrol the al-Saleheen neighborhood in eastern Aleppo on December 12. GEORGE OURFALIAN/AFP/Getty Images
Rebels in southeastern Aleppo target government forces with anti-aircraft weaponry on December 12. STRINGER/AFP/Getty Images
Civilians flee the Sukkari neighborhood in southeastern Aleppo on December 12. STRINGER/AFP/AFP/Getty Images
Pro-government forces patrol Aleppo's Sheikh Saeed district on December 12 after it was recaptured from rebel forces. GEORGE OURFALIAN/AFP/Getty Images
In this handout photo from the International Committee for the Red Cross, women displaced from eastern Aleppo gather at a shelter in the village of Jibreen, south of Aleppo, on December 12. ICRC/AP
Smoke rises from the Bustan al-Qasr neighborhood on December 12. STRINGER/AFP/Getty Images
Civilians from eastern Aleppo stream into a government checkpoint at the al-Hawoz street roundabout on Saturday, December 10. GEORGE OURFALIAN/AFP/Getty Images
Rebel fighters take aim at pro-government positions in Aleppo on Friday, December 9. THAER MOHAMMED/AFP/Getty Images
Syrian rebels walk down a street in eastern Aleppo on December 9. THAER MOHAMMED/AFP/Getty Images
Clouds of smoke billow from eastern Aleppo's al-Shaar neighborhood on Monday, December 5. GEORGE OURFALIAN/AFP/Getty Images