Syrian regime forces attack a pre-school in Aleppo [Getty Images]

ALEPPO, SYRIA - MAY 3: A man carries a wounded boy into an ambulance following a barrel bomb attack of Syrian regime forces on an opposition-controlled pre-school in Salahaddin region in Aleppo, Syria on May 3, 2015. (Photo by Ahmed Muhammed Ali/Anadolu Agency/Getty Images) — see more

ALEPPO, SYRIA - MAY 3: A man carries a wounded boy into an ambulance following a barrel bomb attack of Syrian regime forces on an opposition-controlled pre-school in Salahaddin region in Aleppo, Syria on May 3, 2015. (Photo by Ahmed Muhammed Ali/Anadolu Agency/Getty Images)

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