From the U.S. State Department:
The Department of State warns U.S. citizens of the risks of traveling to Libya and strongly advises against all but essential travel to Tripoli and all travel to Benghazi, Bani Walid, and southern Libya, including border areas and the regions of Sabha and Kufra. Because of ongoing instability and violence, the Department’s ability to provide consular services to U.S. citizens in these regions of Libya is extremely limited. ...
The Embassy’s website includes consular information and the most recent messages for U.S. citizens in Libya. U.S. citizens in need of emergency assistance should call 091-379-4560 within Libya or 218-91-379-4560 if dialing from outside of Libya.
For information on “What the Department of State Can and Can't Do in a Crisis,” please visit the Bureau of Consular Affairs’ Emergencies and Crisis link. Up-to-date information on security can also be obtained by calling 1-888-407-4747 toll-free in the United States and Canada or, for callers outside the United States and Canada, on a regular toll line at 1-202-501-4444. These numbers are available from 8:00 a.m. to 8:00 p.m. Eastern Daylight Time, Monday through Friday (except U.S. federal holidays).
For further information, U.S. citizens should consult the Department of State’s Country Specific Information for Libya. 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