From the U. S. State Department:

The Department of State warns U.S. citizens of the risks of travel to Chad and recommends U.S. citizens avoid all travel to eastern Chad and border regions. High levels of violent crime and a continuing risk of clashes between the Chadian government and armed groups exist in these areas. In particular, there is a heightened risk of carjacking and kidnapping for ransom within these conflict zones. The U.S. Embassy in Chad has prohibited travel by official U.S. government personnel to all areas outside the capital, N’Djamena, and its immediate environs without express advance authorization. U.S. citizens affiliated with humanitarian relief efforts should review security precautions and consider measures to mitigate exposure to violent crime. U.S. citizens residing in Chad should exercise caution throughout the country. ...

U.S. State Department Warning