A family mourns the loss of their relatives to what activists say was a barrel bomb dropped by forces loyal to Syria's President Bashar al-Assad, in Aleppo's al-Fardous district April 29, 2015. REUTERS/Hosam Katan TPX IMAGES OF THE DAY

Men react at a site hit by what activists say was a barrel bomb dropped by forces loyal to Syria's President Bashar al-Assad, in al-Kalaseh neighbourhood in Aleppo April 29, 2015. REUTERS/Hosam Katan 

A man reacts at a site hit by what activists say was a barrel bomb dropped by forces loyal to Syria's President Bashar al-Assad, in Aleppo's al-Fardous district April 29, 2015. REUTERS/Hosam Katan 

A dust-covered civil defense member walks at a site hit by what activists say was a barrel bomb dropped by forces loyal to Syria's President Bashar al-Assad, in Aleppo's al-Fardous district April 29, 2015. REUTERS/Hosam Katan 

A man carries a child at a site hit by what activists say was a barrel bomb dropped by forces loyal to Syria's President Bashar al-Assad, in al-Kalaseh neighbourhood in Aleppo April 29, 2015. REUTERS/Hosam Katan 

Civilians inspect a site hit by what activists say was a barrel bomb dropped by forces loyal to Syria's President Bashar al-Assad, in Aleppo's al-Fardous district April 29, 2015. REUTERS/Mahmoud Hebbo 

Civil defense members and residents gather at a site hit by what activists say was a barrel bomb dropped by forces loyal to Syria's President Bashar al-Assad, in Aleppo's al-Fardous district April 29, 2015. REUTERS/Mahmoud Hebbo 

A mother and her son mourn the loss of their relatives caused by what activists say was a barrel bomb dropped by forces loyal to Syria's President Bashar al-Assad, in Aleppo's al-Fardous district April 29, 2015. REUTERS/Mahmoud Hebbo 

A man walks on debris as members of the civil defense use a front loader to remove rubble at a site hit by what activists say was a barrel bomb dropped by forces loyal to Syria's President Bashar al-Assad, in Aleppo's al-Fardous district April 29, 2015. REUTERS/Mahmoud Hebbo 

A man reacts at a site hit by what activists say was a barrel bomb dropped by forces loyal to Syria's President Bashar al-Assad, in Aleppo's al-Fardous district April 29, 2015. REUTERS/Mahmoud Hebbo 

A woman reacts as other civilians inspect a site hit by what activists say was a barrel bomb dropped by forces loyal to Syria's President Bashar al-Assad, in Aleppo's al-Fardous district April 29, 2015. REUTERS/Mahmoud Hebbo 

A man cries as he is comforted by another at a site hit by what activists say was a barrel bomb dropped by forces loyal to Syria's President Bashar al-Assad, in Aleppo's al-Fardous district April 29, 2015. REUTERS/Mahmoud Hebbo 

A man carries two children at a site hit by what activists say was a barrel bomb dropped by forces loyal to Syria's President Bashar al-Assad, in al-Kalaseh neighbourhood in Aleppo April 29, 2015. REUTERS/Hosam Katan 

Men inspect the damage at a site hit by what activists say was a barrel bomb dropped by forces loyal to Syria's President Bashar al-Assad, in al-Kalaseh neighbourhood in Aleppo April 29, 2015. REUTERS/Hosam Katan 

A father and his daughter mourn the loss of their relatives to what activists say was a barrel bomb dropped by forces loyal to Syria's President Bashar al-Assad, in Aleppo's al-Fardous district April 29, 2015. REUTERS/Hosam Katan