BEIRUT (Reuters) – Rebels in Aleppo have agreed to form a new military alliance to better organize the defense of parts of the city they control from a ferocious assault by the government and its allies, officials in two of the insurgent groups said on Thursday.

The Syrian government assault backed by allied militia has driven the rebels from more than a third of the territory they held in eastern Aleppo, threatening to crush the rebellion in its most important urban stronghold.

Rivalry among rebel groups has been seen as one of their major flaws throughout the war.

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