The organisation says there is evidence of "systematic abuse" of civilians by government forces, including unlawful killings and torture.
It has urged the Arab League to suspend Syria when it meets to discuss the crisis at an emergency meeting this weekend.
The group has also called for the UN Security Council to impose sanctions and an arms embargo on the Syrian regime.
Its report focuses on violations by the Syrian security forces between April and August, when 587 civilians were killed in the city of Homs and the surrounding governate. Read More