In a statement, the COI said it had "allegations of opposition groups... Preventing civilians from leaving as well as opposition fighters embedding themselves within the civilian population, thus heightening the risk to civilians of being killed or injured".
It specifically implicated Al-Qaeda's former affiliate Fateh al-Sham Front, and the powerful Ahrar al-Sham rebel group.
The COI, an independent investigative body set up by the UN in 2011, collects evidence on human rights law violations committed during Syria's civil war.
Since then, government troops and their allies have waged a brutal offensive on Syria's second city pushing the rebel resistance to the brink of collapse.
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The COI also noted the grave allegations levelled against pro-government forces in Aleppo, including "summary executions, arbitrary arrests, enforced disappearances and forced conscription".
The commission said Syrian President Bashar al-Assad's government was now in "effective control" of eastern Aleppo, a former rebel stronghold, and therefore had "primary responsibility" for ensuring that violations in the city are stopped.
"At this critical moment, the illusion that military victory is still possible must be discouraged," the commission's statement said.
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