Among the findings, the UN said Syria deliberately bombed a humanitarian convoy in Aleppo and used chlorine bombs. Rebels were also found to have used civilians as human shields.
All sides battling in Aleppo last year committed war crimes, including Syrian government aircraft deliberately bombing a humanitarian convoy and separately using prohibited chorine chemical munitions, the UN said on Wednesday.
The United Nations Commission of Inquiry (COI) for Syria report - released as peace talks continue in Geneva - documented numerous war crimes between July and late December, when Aleppo fell to pro-government forces after months of siege and "daily air strikes" by the Syrian air force and its Russian ally.
In addition to Russian and government aircraft indiscriminately bombing hospitals, markets and residential buildings, the Syrian air force dropped "toxic industrial chemicals, including chlorine," the report found. There was no evidence Russia carried out chemical attacks.
Hundreds of people were killed and wounded in the five month siege, which turned the tide of the nearly six-year war in favor of the Syrian regime.
UN investigators also said for the first time there was strong evidence Syrian warplanes "meticulously planned and ruthlessly carried out" bombing of a humanitarian convoy on September 19. The bombing killed at least 10 aid workers and slowed down humanitarian deliveries to civilians trapped in rebel-held eastern Aleppo.
Syrian warplanes in September deliberately targeted 18 aid lorries near the town of Orum al-Kubra, Aleppo province, the UN said.
The Syrian government has denied the aid convoy bombing, blaming it on terrorists. An earlier UN investigation in December said it was unable to establish blame. But after examining satellite images, forensic evidence and other material the UN panel found "Syrian air forces targeted (the) humanitarian aid convoy."
However, the UN report found rebels, including the including former al-Qaeda affiliate Fatah al-Sham Front, indiscriminately lobbed artillery shells into government-held western Aleppo in what amounted to a war crime. Rebels also attacked the Kurdish-controlled Sheikh Maqsoud district, in another war crime.
As government allied forces closed in on eastern Aleppo, some armed groups prevented civilians from fleeing and used them as "human shields," the report said, confirming Syrian regime and Russian claims.
Aleppo victim of war crimes
The Syria COI, established in 2011 to investigate war crimes, described citizens in Aleppo as the "victim to war crimes committed by all parties."
The fight over Aleppo ended after an evacuation deal was reached to move rebels and civilians to western Aleppo or opposition-controlled Idlib province. The evacuations were monitored by the UN and the International Committee of the Red Cross, but the Syria COI said it left "no option to remain."
"Such agreements amount to the war crime of forced displacement of the civilian population," UN investigators concluded.
In the final days of the battle, both Syrian government allied forces and rebels carried out reprisal killings, investigators said. The Syrian army is backed by Hezbollah, Russian, Iranian and Iraqi fighters, but the COI did not link any specific groups to the war crimes.
cw/jm (AFP, dpa, Reuters)