The Elders, a peace advocacy group founded by Tutu and former South African President Nelson Mandela, said Thursday at least 1,000 people have been killed in the Bangui, the CAR capital, in the past two months.
Tutu said the methods used by Christian militia anti-balaka and Sunni rebel coalition Seleka were appalling.
"The reports of sexual violence, recruitment of child soldiers and other grave abuses, including the beheading of children, are absolutely ghastly," he said in a statement.
The International Criminal Court said earlier this month it was opening an investigation into atrocities committed in CAR. U.N. officials this week said it was the Christian militia that was responsible for most of the violence.
Essam el-Sayed, a surgeon working for the International Committee of the Red Cross, said Tuesday the wounds he has treated were gruesome.
"It's proof of deep hatred [between religious communities]," he said in a statement.
The French government last week ordered a deployment of troops to the former French colony to help support an African Union peacekeeping mission in CAR.