Seleka, a Sunni Muslim rebel coalition, overthrew the government in March. Chaos ensued when former President Michel Djotodia lost control of the rebel force. The crisis sparked attention from the International Criminal Court when anti-balaka, a Christian militia, took up arms against their Muslim rivals.
Pillay said in a statement that, although some Seleka supporters continue to target Christians, "most of the ongoing human rights violations are being committed by anti-balaka elements, which appear to be growing more organized by the day."
Pillay said members of anti-balaka are deliberately targeting members of the Sunni population in so-called cleanup operations in the capital Bangui and elsewhere.
"Although the overall situation seems slightly calmer in Bangui, reports of more killings and violence continue," she said.
The French government said Friday it was sending another 400 troops to CAR, a former French colony, to ensure "all enemies of peace" are fought effectively to bring stability to the country.