The battle, "a stage of unrelenting violence", saw Syrian government forces, backed by Russian Federation, conducting daily airstrikes and using chlorine bombs in residential areas while rebel groups in some cases deliberately attacked civilians and used them as human shields.
The UN also accused Damascus of repeatedly using chemical weapons and cluster munitions.
The 37-page report by the UN Commission of Inquiry on Syria - released on Wednesday as Syrian peace talks continue in Geneva - covers the July-December 2016 period and capture of Aleppo by forces supporting the Syrian regime.
Both sides in the battle for Aleppo in Syria a year ago committed war crimes, according to a United Nations investigation released Wednesday.
As part of a strategy to force those inside the city's rebel-held east to surrender, pro-government forces imposed a siege in late July, trapping civilians without adequate food or medical supplies, and stepped up an aerial campaign. From July 21, 2016 to December 22, when government troops recaptured the city, the Syrian air force and its Russian ally "conducted daily air strikes" on Aleppo, the COI said.
The report also said Syria's air force used chemical weapons - chlorine gas - against residential areas.
The report examined the September bombing of a United Nations humanitarian aid convoy by the Syrian Air Force in the Aleppo countryside, which killed more than a dozen aid workers and destroyed "vital supplies" intended for needy civilians.
"The munitions employed (against the convoy) were particularly appropriate for attacking unarmored vehicles and individuals", the report said.
"Within the last 24 hours the Russian Centre for reconciliation of opposing sides has held 7 humanitarian events in the provinces of Aleppo (6) and Homs (1)", the statement says, adding that overall 4,700 Syrians received humanitarian aid the total weight of which amounted to 4.95 tonnes.
"In none of the incidents investigated by the commission were military targets identified as being present in or around the vicinity of a hospital, nor were warnings given prior to any given attack as required by global humanitarian law".
The commission also found the "intentional" targeting of medical facilities to be war crimes.
The report focused on the M10 hospital, in al-Sakhour district, which it said was hit four times between late September and mid-October, putting it completely out of service.
The researchers used CCTV footage from inside M2 to piece together the effects of the attacks.
"A deliberate attack against them such as the one that took place in Orum al-Kubra amounts to war crimes and those responsible must be held accountable for their actions", said Commissioner Carla del Ponte.
Western Aleppo, which was controlled by Syrian government forces, had been shelled by opposition groups, it added, resulting in numerous deaths and injuries.
The report says the attacks were launched without a clear military target and intentionally terrorised the civilian population, constituting a war crime. They also prevented civilians from leaving eastern Aleppo and used them as "human shields".
Syrian aircraft used chlorine - a chemical agent prohibited under worldwide law - against the civilian population of eastern Aleppo, causing significant physical and psychological harm to hundreds of civilians.