From the U.S. State Department:

The U.S. Department of State continues to warn U.S. citizens of the risks of travel to Eritrea and strongly recommends U.S. citizens defer all travel to the country. This replaces the Travel Warning dated February 27, 2011, updates information on security incidents, including piracy, and reminds U.S. citizens of ongoing security concerns in Eritrea.

The Eritrean government continues to restrict the travel of all foreign nationals. These restrictions require all visitors and residents, including U.S. diplomats, to apply 10 days in advance for permission to travel outside Asmara's city limits. Permission is rarely granted. As a result, the U.S. Embassy is extremely limited in its ability to provide emergency consular assistance outside of Asmara.

U. S. State Department Warning