"It is essential that such serious allegations be investigated thoroughly and impartially by all sides. If found to be true, those responsible must be brought to justice."
The human rights group said both countries should call for a public inquiry by the International Humanitarian Fact-Finding Commission, a permanent body of 15 international experts set up by the Geneva Convention, into the conflict.
Russian forces moved into Georgia on August 8 to repel a Georgian military attempt to retake South Ossetia, which has received extensive backing from Moscow.
Under an EU-brokered ceasefire, Russian forces later withdrew to within South Ossetia and another separatist Georgian region, Abkhazia, which Moscow has recognised as independent states.
But Tbilisi had accused Russia of not respecting the ceasefire by keeping forces in Perevi and in the disputed Akhalgori district, an area that was under Georgian control before the war.