The rights group accuses both security forces and local Rakhine Buddhists of carrying out attacks against Rohingyas in the region and says an unknown number have been beaten, killed and raped.
The group's Asia researcher, Benjamin Zawacki, says while both Buddhists and Muslims have been targeted, recent violence has been directed primarily against Rohingyas.
Tensions between the Rakhines and the Rohingyas are longstanding, partly because many Rakhines consider Rohingyas to be illegal settlers from neighboring Bangladesh.
The government says clashes in May and June left at least 78 people dead. A state of emergency was declared June 10.