The Regional Security Officer (RSO) is the senior security official at a U.S. diplomatic mission, drawn from the Diplomatic Security Service (DSS), a bureau of the U.S. Department of State. The RSO advises the Chief of Mission on all security matters and is responsible for the physical protection of the embassy compound, the safety of American personnel and their dependents, and the integrity of classified information. Typical duties include managing local guard forces, coordinating with host-nation police and intelligence services, conducting threat assessments, overseeing residential and travel security, running anti-terrorism and active-shooter drills, and investigating passport and visa fraud.
RSOs also serve as the principal law-enforcement liaison between the United States and host-country authorities, often facilitating cooperation on transnational crime, fugitives, and counterterrorism cases. At larger posts, the RSO supervises Assistant Regional Security Officers (ARSOs) and Marine Security Guards from the Marine Corps Embassy Security Group, who provide internal post security.
The role gained heightened public attention after the 1998 East Africa embassy bombings in Nairobi and Dar es Salaam and the 2012 attack on the U.S. Special Mission in Benghazi, both of which led to reviews of overseas security posture — most notably the Accountability Review Boards mandated under the Omnibus Diplomatic Security and Antiterrorism Act of 1986 (the law that created the modern DSS following the Inman Report).
While Regional Security Officer is specifically a U.S. State Department title, many foreign ministries maintain analogous positions (e.g., the UK Foreign, Commonwealth & Development Office's Overseas Security Manager). RSOs are armed federal agents and retain full law-enforcement authority under U.S. law, though their operational activities abroad are governed by host-country agreements and the Vienna Convention on Diplomatic Relations (1961).
Example
After the 2012 Benghazi attack, the Accountability Review Board examined whether the Regional Security Officer's staffing requests for the Special Mission had been adequately resourced by Washington.