From the U.S. State Department:

The Department of State warns U.S. citizens of the risks of traveling to Sudan, urges U.S. citizens to avoid all travel to the Darfur region of Sudan, the Blue Nile and Southern Kordofan States, and advises you to consider carefully the risks of travel in other areas of Sudan. On September 15, 2012, the Department of State ordered the departure of all dependents of U.S. direct hire personnel and all non-emergency U.S. government personnel from Sudan, following the attack on the U.S. Embassy in Khartoum. This Travel Warning replaces the Travel Warning issued on September 7, 2012.

While the Government of Sudan has taken some steps to limit the activities of terrorist groups, elements of these groups remain in Sudan and have threatened to attack Western interests. The terrorist threat level throughout Sudan, and particularly in the Darfur region, remains critical, and the U.S. Embassy has implemented enhanced security measures to protect U.S. government personnel assigned to Sudan. These measures include requiring U.S. government personnel to travel in armored government vehicles for official business, and to obtain advance permission for travel outside of Khartoum. In addition, family members under age 21 of U.S. Embassy personnel are not allowed to reside in Sudan. ...

U.S. State Department Warning