Most Muslims have been expelled from western Central African Republic (CAR), where thousands of civilians are at risk of being killed "right before our eyes," U.N. High Commissioner for Refugees Antonio Guterres said Thursday. "Since early December, we have effectively witnessed a 'cleansing' of the majority of the Muslim population in western CAR," Guterres said at a U.N. Security Council meeting on the country. "Tens of thousands of [Muslims] have left the country, the second refuge outflow of the current crisis, and most of those remaining are under permanent threat," Guterres told the 15-country council, which is considering a U.N. proposal for a 12,000-strong peacekeeping force to prevent the country from falling into possible genocide. "Just last week, there were about 15,000 people trapped in 18 locations in western CAR, surrounded by anti-Balaka elements and at very high risk of attack," Guterres said. "International forces are present in some of these sites, but if more security is not made available immediately, many of these civilians risk being killed right before our eyes." Guterres said that until last year, CAR "was largely a stranger to religious conflict." But the worsening violence has enabled armed groups to use religion as a pretext for violence.