Posted: 3:23 am EDT
Update #1: 7:02 pm EDT
Update #2: March 25, 12:27 am EDT
Update #3: 12:25 pm EDT
Update #4: 3:51 pm EDT
Update #5: 5:57 pm EDT
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Updated: 7:02 pm EDT: We understand that there are two individuals with the State Department who are unaccounted for in Brussels at this time. We will update when we learn more.

Updated: March 25, 12:27 am EDT: One of the two State Department individuals still missing in Brussels is a family member and part of mission under Chief of Mission authority. The second one is reportedly USG but is not part of the tri-mission (we don’t know at this time if employee or family member). 

Update #3: 12:25 am EDT: One is a family member and reportedly part of the USNATO mission; the second one who is USG but is not part of the tri-mission is also a family member.  

Update #4: 3:51 pm EDT:  The two unaccounted for are now the first two confirmed USG fatalities in Brussels. According to the AP  the State Department has confirmed that the families of two Americans had been informed of their deaths in the attacks Tuesday. Spokeswoman Elizabeth Trudeau said the names were being withheld out of privacy considerations. 

Update #5: 5:57 pm EDT: According to ABCNews, the two Americans killed in Brussels this week have been confirmed as the spouses of U.S. personnel. “A U.S. official confirmed to ABC News that the two Americans were living in Europe at the time of the attacks. Their names have not been released and the families have asked for privacy.”

Via state.gov | Mark C. Toner, Deputy Spokesperson, Daily Press Briefing, March 23, 2016:

“So in terms of State Department or U.S. Government personnel, that is still also ongoing. We still have not accounted for every official U.S. Government employee or their members – or family members on the ground in Belgium – or in Brussels, rather. Partly, that reflects the size of the mission or three missions. There’s a bilateral mission, there’s a mission to the EU, as well as a mission to NATO. And as I said, partly reflects the fact that there’s a number of injured in the hospital – in hospitals around the city, and we’re still trying to gain access and trying to determine the identity of those and the nationality, obviously, of those individuals.”

The Brussels Tri-Mission includes U.S. Embassy Brussels, the U.S. Mission to the European Union (USEU), and the U.S. Mission to the North Atlantic Treaty Organization (USNATO). Each mission has its own ambassador and DCM. Posts often have an administrative “warden” system for the official U.S. citizen community.  Shortly after the attacks, the mission’s or tri-mission’s phone tree/notifications would have been activated. But we should also note that the Tri-Mission has one of the heaviest visitor workloads in the world due to the num­ber of U.S. agencies that conduct business in Brussels.