The U.N. Human Rights Council said at least 40 people were reported killed since Friday in Bangui, the CAR capital.
U.N. High Commissioner for Human Rights Navi Pillay said CAR is at risk of "massive violations" unless there is serious intervention in the crisis.
"Despite some important reconciliation efforts in Bangui, the situation remains extremely volatile and dangerous," she said in a statement Tuesday.
Prime Minister Nicolas Tiangeye and President Michel Djotodia agreed last week to resign. Djotodia commanded the rebel Seleka coalition, which toppled the CAR government last year, but quickly lost control of the situation.
Conflict in CAR took on a religious tone when members of a Christian militia known as anti-balaka took up arms against rebels from Seleka, a Sunni group.
Pillay's office said a four-member team spent two weeks in CAR last month assessing the situation. There, they witnessed a cycle of violence that included the use of rape as a weapon of war, mutilations, extrajudicial killings and other grave violations of international law.
Interim Prime Minister Alexandre Ferdinand Nguendet is tasked with organizing new elections in CAR.