From the U.S. State Department:
The Department of State warns U.S. citizens against all travel to the Central African Republic (CAR) and recommends that those who remain in CAR depart immediately by taking advantage of existing commercial flights. U.S. citizens who have decided to stay in CAR despite this warning should review their personal security situation and seriously consider departing. ...
For information on general crime and security issues, you should also consult the Department of State Country Specific Information for the Central African Republic; as well as The Worldwide Caution; located on the Bureau of Consular Affairs website.
U.S. State Department Warning