US military Joint Base Andrews, just outside of Washington, was on Thursday put on lockdown following reports of an active shooter at a medical centre.
Known as "America's airfield", Andrews is the home base of Air Force One, the airplane used by the US presidents. A "shelter in place" order was in effect at the base.
The shooter was barricaded on the third floor of the medical centre, according to a reporter for the military newspaper Stars and Stripes.
There appeared to be some confusion whether the situation was real or part of a scheduled exercise. Base officials said the call came during an exercise but the report was real.
"We are reacting to a report of a real-world active shooter," a spokesperson for the base told WTTG TV.
"The call occurred during an exercise. Because the report came in as a real active shooter, we have to respond accordingly. We are treating as if it is and no further information at this time."
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