From the U. S. State Department:
The Department of State warns U.S. citizens of the risks of travel to Chad and recommends citizens avoid all travel to eastern Chad and border regions. Because of security concerns, the U.S. Embassy in Chad reviews all proposed travel by official U.S. government personnel to areas outside the capital, N'Djamena, and its immediate surroundings before approving such arrangements. U.S. citizens affiliated with humanitarian relief efforts similarly should review security precautions and consider measures to mitigate exposure to violent crime and other threats. ...
Embassy updates are available at the U.S. Embassy N'Djamena web site. The current Worldwide Caution, Travel Warnings, Travel Alerts, and Country Specific Informationas well as global updates are available at the U.S. Department of State's Bureau of Consular Affairs. Travelers may obtain up-to-date information on security conditions by calling 1-888-407-4747 toll free in the United States and Canada, or from other countries on a regular toll-line at 1-202-501-4444.
U.S. State Department Warning