A Syrian man reacts while standing on the rubble of his house while others look for survivors and bodies in the Tariq al-Bab district of the northern city of Aleppo on February 23, 2013.
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A Free Syrian Army fighter aims his weapon during clashes with government forces in Aleppo on Tuesday, January 15, 2013.
A member of the Syrian pro-government forces stands amid heavily damaged buildings in Aleppo's 1070 district on November 8, 2016, after troops seized it from rebel fighters.
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A wounded Syrian boy cries after bombs fell on the opposition-controlled Firdevs neighborhood in Aleppo on October 11, 2016.
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Smoke rises after a bomb explodes in a residential area in the Darat Izza neighborhood of Aleppo on October 4, 2016.
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Search and rescue team members carry an injured man after Syrian regime airstrikes targeted the Meshed neighborhood of Aleppo on July 21, 2016.
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A rebel fighter aims his weapon toward Syrian government forces' positions at the Menagh military airport near Aleppo on March 13, 2013.
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The body of a Syrian army soldier lies on the ground after heavy clashes with government forces at a military academy besieged by the rebels in Tal Sheer village, north of Aleppo, on December 16, 2012.
Debris covers a street and flames rise from a building after a reported airstrike by Syrian government forces on March 7, 2014, during the Friday prayer in the Sukkari neighborhood of Aleppo.
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Wounded 5-year-old Omran Daqneesh sits alone in the back of an ambulance after he was injured during a Russian or Assad regime forces airstrike targeting the Qaterji neighborhood of Aleppo on August 17, 2016.
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A Syrian opposition tank fires a rocket toward an Assad forces' building during clashes near the Air Intelligence building of Jamiat al-Zahra, Aleppo, on April 13, 2015.
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On September 7, 2012, Free Syrian Army fighters run after attacking a Syrian army tank during fighting in the Izaa district of Aleppo.
Search and rescue team members inspect collapsed buildings after Assad regime forces attacked residential areas in the Karm al-Beik region of Aleppo on July 9, 2015.
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Syrian civil defense volunteers and rescuers remove a baby from under the rubble of a destroyed building after a reported airstrike on the rebel-held neighborhood of al-Kalasa in Aleppo on April 28, 2016.
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A Free Syrian Army fighter takes cover during clashes with Syrian army soldiers in the Salaheddine neighborhood of central Aleppo on August 7, 2012.
Syrian pro-government forces walk in the damaged ancient Umayyad Mosque in the old city of Aleppo on December 13, 2016, after they captured the area.
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A man in front of a field hospital mourns the death of his relatives on August 21, 2012, in Aleppo.
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Rubble is seen in the Salaheddine neighborhood on March 24, 2013, in Aleppo.
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Syrian government forces walk in the strategic area of the Bazo hilltop, on the southern outskirts of Aleppo, as they advance to seize the rebel-held eastern part of the city on October 25, 2016.
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An aerial view shows a convoy of buses and ambulances waiting at a crossing point in the Amiriyah district of Aleppo on December 15, 2016, to evacuate civilians trying to flee from areas under siege by Iran-led Shiite militias and Assad regime forces.