Its account of the convoy attack went much further than findings of a United Nations inquiry set up by then-Secretary General Ban Ki-moon, which concluded in December that the convoy had been bombed from the air but did not identify the attackers.
The 31-truck convoy organized by the United Nations and the Syrian Arab Red Crescent had been carrying food, medicine, children’s clothes and other humanitarian supplies destined for families in opposition-controlled areas and had been traveling with the government’s knowledge and permission.
The government of President Bashar al-Assad had no immediate comment on the new report, but it has repeatedly denied responsibility for the convoy assault or any other war crimes in the conflict, which Mr. Assad regards as a battle against terrorism.
Syrian officials and their Russian allies have suggested that insurgents were responsible for hitting the convoy, or perhaps even warplanes from the American-led coalition that has been bombing Islamic State targets in Syria. The Americans, who operate in areas far from the convoy assault site, have called such suggestions absurd.
The report released Wednesday found that war crimes had been committed by government and rebel forces, corroborating many of the worst allegations that Aleppo residents had made against both sides.
For months, the Syrian forces and their Russian allies bombarded eastern Aleppo as part of a strategy to force surrender, the commission’s chairman, Paulo Pinheiro, told reporters in Geneva, expressing frustration that the Syrian government had not cooperated with the investigation.
Mr. Pinheiro denounced what he called “the deliberate targeting of civilians” that killed many, including hundreds of children.
The Syrian government and Russia mainly used unguided, indiscriminate munitions on civilian areas, killing 300 people, including 96 children, in the first four days of a September offensive alone, the report said.
The report found that government forces had hit hospitals; used internationally banned chlorine gas and cluster munitions; arrested fleeing civilians; and carried out summary executions, with some soldiers killing their own relatives.
On the other side, the report found that rebel groups had indiscriminately shelled government-held civilian areas with no specific military target, killing dozens, including women and children. In rebel areas, the report said, some groups prevented people from evacuating and discriminated in food distribution during a siege, favoring relatives and supporters.
Strikingly, the report also found that evacuations of besieged civilians from rebel-held eastern Aleppo and from the government-held towns of Fouaa and Kfarya during the battle constituted the war crime of forced displacement, because residents had no choice and were moved for “strategic reasons,” not safety.
The report could further complicate the challenges facing a special United Nations mediator, Staffan de Mistura, who is seeking to bring government and opposition representatives together in Geneva to discuss a political settlement.
Global powers that back opposing sides in the six-year-old conflict still find themselves unable to agree on basic facts, let alone hold war crime perpetrators accountable.
The report found that government aircraft repeatedly used chlorine bombs in Aleppo, violating a global treaty banning chemical weapons that Syria has signed. Just a day before the report was released, Russia and China vetoed a Security Council resolution to impose sanctions on some senior Syrian military officials and government bodies for using chemical weapons earlier in the conflict.
And the illegal tactics outlined in the report have appeared to continue throughout the week, further undermining the fragile efforts in Geneva. Airstrikes have crippled hospitals in Idlib and the Damascus suburbs. Heavy bombardment has hit civilian areas in Douma and the Homs suburb of Al Waer.
The strikes in Al Waer were said to have been in response to an attack by gunmen and suicide bombers on two security headquarters facilities in Homs, which killed 42 people. The hard-line Islamist group Tahrir al-Sham, a coalition that includes Syria’s Qaeda affiliate and is not a party to the talks in Geneva, claimed responsibility.
The United Nations researchers found no evidence that Russia had used chemical weapons. They also did not receive sufficiently clear evidence to directly tie Russian forces to any war crimes described in the report.
But they said Russian aircraft had joined the Syrian air force in using indiscriminate weapons in a deadly campaign that repeatedly targeted hospitals, water distribution stations, markets and bakeries and suggested “a willful disregard” for the international laws of war.
Government aircraft, the commission said, had carried out repeated attacks with barrel bombs laced with chlorine gas in the five months covered by the report, from July 21 to Dec. 22, violating an international ban on chemical weapons.
The report drew on 291 interviews, many conducted remotely with former residents of Aleppo still in Syria, as well as satellite imagery, medical records and communications with governments and nongovernmental organizations.
The commission report, its 13th on the conflict, followed a directive by the Human Rights Council in October to identify those responsible for abuses in the battle for Aleppo.