From the U.S. State Department:
The U.S. Department of State warns U.S. citizens of the high security threat level in Yemen due to terrorist activities and civil unrest. The Department urges U.S. citizens to defer travel to Yemen and those U.S. citizens currently living in Yemen to depart. …
The U.S. Embassy in Sana'a is located at Dhahr Himyar Zone, Sheraton Hotel District, P.O. Box 22347. The telephone number of the Consular Section is (967)(1)755-2000, extension 2153 or 2266. For after-hours emergencies involving U.S. citizens, please call (967)(1)755-2000 (press zero for extension) or (967) 733-213-509. From time to time the Embassy may temporarily close or suspend public services for security reasons. Emergency assistance to U.S. citizens during non-business hours (or when public access is restricted) is available through Embassy duty personnel.
For the latest security information, U.S. citizens living and traveling abroad should regularly monitor the State Department's Bureau of Consular Affairs website where the current Worldwide Caution, Travel Alerts and Travel Warnings, and Country Specific Information for Yemen can be found. 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 in other countries, by calling a regular toll line at 1-202-501-4444. These numbers are available 8:00 a.m. to 8:00 p.m. Eastern time, Monday through Friday (except U.S. federal holidays).
U.S. State Department Warning