Syrian rebels and civilians in the besieged eastern half of Aleppo are bracing for an onslaught ground assault by Syrian regime forces and their Shia fighter allies which could once and for all end the opposition’s resistance in the city.

US officials said they were seeing signs that thousands of troops from across the Shia world - including Syrian regime soldiers, Iranian Revolutionary Guards, Hizbollah fighters, Iraqi militiamen and Afghan mercenaries - were massing for a final assault on Aleppo.