The U.S. Embassy in Asmara does not process Immigrant Visas. All Immigrant Visas for Eritreans  are handled at the U.S. Embassy in Addis Ababa or Nairobi.

A permanent resident (called lawful permanent resident or LPR) or conditional resident (CR) who has remained outside the United States for longer than one year, or beyond the validity period of a Re-entry Permit, will require a new immigrant visa to enter the United States and resume permanent residence.  You can learn more about Returning Resident Visas on usvisas.state.gov.