From the U. S. State Department:
The Department of State warns U.S. citizens of the risks of travel to Nigeria and recommends that U.S. citizens avoid all travel to Adamawa, Borno, and Yobe states because of the proclamation on May 14, 2013, by the government of the Federal Republic of Nigeria of States of Emergency in those three states. The ability of the Mission to provide assistance to U.S. citizens in those states remains severely limited. The Department also continues to recommend against all but essential travel to the following states due to the risk of kidnappings, robberies, and other armed attacks: Abia, Akwa Ibom, Bauchi, Bayelsa, Delta, Edo, Gombe, Imo, Jigawa, Kaduna, Kano, Katsina, Kebbi, Niger, Plateau, Rivers, Sokoto, and Zamfara. The Department also warns against travel to the Gulf of Guinea because of the threat of piracy. Based on safety and security risk assessments, the Embassy maintains restrictions for travel by U.S. officials to all northern Nigerian states (in addition to those listed above); officials must receive advance clearance by the U.S. Mission for any travel deemed as mission-essential. U.S. citizens should be aware that extremists could expand their operations beyond northern Nigeria to the country's middle and southern states. ...
Current information on safety and security can also be obtained by calling 1-888-407-4747 toll-free in the United States and Canada, or a regular toll line at-1-202-501-4444 for callers from other countries. These numbers are available from 8:00 a.m. to 8:00 p.m. Eastern Time, Monday through Friday (except U.S. federal holidays). You can also stay up to date by bookmarking our Bureau of Consular Affairs website, which contains the current Travel Warnings and Travel Alerts as well as the Worldwide Caution.
U.S. State Department Warning