A U.N. statement said Christians and Muslims have launched attacks against each other in the past two weeks in and around the capital city of Bangui, where 210,000 people have been driven from their homes.
Nearly 750,000 people -- out of a population of 4.6 million -- have been displaced since the country was thrown into turmoil a year ago, when mostly Muslim rebels launched attacks and forced President Francois Bozize to flee, the U.N. High Commissioner for Refugees' office said.
"In the west of the country, in Bouar, our team witnessed clear attempts to ferment fear and distrust among religious communities, and the reported involvement of armed elements from neighboring countries," said U.N. High Commissioner for Human Rights Navi Pillay.
She cited other incidents, including the reported lynching of 12 Muslims in Bangui in the past 10 days and numerous reports of reprisal attacks.
"These developments are extremely worrisome and should ring alarm bells around the world for sustained and urgent efforts," Pillay added.