Rival groups signed deal aimed at ending over a year of conflict.
U.N. favors a nearly 12,000-strong force aimed at protecting citizens.
Says violence will continue to worsen until peacekeeping force established.
Catherine Samba-Panza has said she will "go to war" with Christian militias who are slaughtering Muslims.
Aid groups say fewer than 10 food wholesalers remain in country.
Communities threatened from reprisal attacks, charity warns.
At least 70 dead and dozens of houses torched in religious clashes.
Reports of revenge attacks as mainly Muslim fighters withdraw from city.
Troops have failed to contain the surging ethnic and religious violence.
French envoy describes the situation as "very, very dire."