New footage emerged of civilians choking in the aftermath of an apparent attack with poison chlorine gas on an opposition-held district as the battle for Syria's biggest city approaches what could be a decisive phase.
Aleppo has been divided for years into government and rebel sectors, but President Bashar al-Assad's army has put the opposition areas under siege and now hopes to capture the whole city in what would be a devastating blow to his enemies.
The arrival of reinforcements from Iraq, where Shi'ite militia are fighting their own war against the Islamic State group, shows how the Syrian and Iraqi conflicts have leapt borders, to become a broad sectarian war across the Middle East.