According to the report, the air raids by the U.S.-led coalition did not, or failed to, take enough measures to distinguish civilians from the military targets.
"Launching indiscriminate attacks that result in death or injury to civilians amounts to a war crime in cases in which such attacks are conducted recklessly," said the report.
The Syrian Democratic Forces (SDF), backed by the U.S., held large-scale operations in Syria which "had led to the near-complete destruction of towns and villages," according to the report.
Syria and Russia were also condemned for their aggression in northwestern Idlib province of Syria.
Turkey and Russia agreed last September to turn Idlib into a de-escalation zone in which acts of aggression are expressly prohibited.
These parties, in the UN report, were accused of targeting health facilities, schools, market areas and agricultural zones, which might amount to "war crimes".
More than 1,000 civilians were killed in and around the Idlib demilitarized zone over the last four months, according to the UN which says further aggression in the city could trigger a humanitarian tragedy "graver than the one experienced in 2015," referring to the mass influx of Syrian refugees to Turkey and Europe.
Syria has just emerged from a devastating civil war that began in 2011.
Since then, hundreds of thousands of people have been killed in the conflict, according to UN figures.
The report also noted that approximately 13 million people has become displaced -- with 6.7 million of migration to abroad and 6.2 million of them turning internally displaced persons (IDP).
Reporter's code: 50101