However, the attack followed months of provocation, and both sides violated international law, the report said.
Russia said the report delivered an "unequivocal answer" on the question of who started the conflict.
But Georgia said the investigation proved that Russia had been preparing for war all along.
The report said about 850 people were killed in the August 2008 war, and that more than 100,000 fled their homes, about 35,000 of whom are still displaced.
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