DAKAR, Senegal — The exodus of tens of thousands of Muslims from Central African Republic amounts to “ethnic cleansing,” a top U.N. official and Amnesty International said Wednesday. The rights group warned that the sectarian bloodshed now under way despite the presence of thousands of peacekeepers is a “tragedy of historic proportions.”

In a visit to the lawless capital of Bangui, the U.N. High Commissioner for Refugees Antonio Guterres said “ethnic-religious cleansing” threatened to tear apart the country, and he called for the international community to help the nation’s nascent interim government restore order.

to say ‘never again.’ This, we have said so many times,” United Nations Secretary-General Ban Ki-moon said late Tuesday. “We must act concertedly and now to avoid continued atrocities on a massive scale.”

More than 1,000 Christians and Muslims have been killed since sectarian fighting erupted in early December and nearly 1 million in this country of 4.6 million have fled their homes.

Amnesty’s use of the term “ethnic cleansing” is among the strongest language invoked yet to describe the violence.