OCHA Director of Operations John Ging said the situation in CAR is deteriorating quickly toward state failure.
"There has been a complete breakdown of law and order and the first priority is protection and the restoration of security and stability," he said in a statement Tuesday. "The atrocities against civilians are indescribable."
The rebel Seleka coalition, which toppled the government this year, is suspected of committing war crimes in the country, prompting the International Criminal Court to investigate.
Ging said there's a "new dimension" to the crisis affecting one of the poorest nations in the world.
"We see incitement of religious communities against each other," he said. "This is sowing the seeds of a profoundly dangerous development."
Interim Prime Minister Nicolas Tiangaye told the U.N. General Assembly last month the war-torn country was on the verge of collapse.
A United Nations resolution backed in October by former colonial power France outlined a new peacekeeping force in CAR and called on the interim government to stick to plans for elections in early 2015.