UPDATE: It appears this was a false alarm:
BREAKING: Official: No evidence of shooting, no arrests, no weapons after report of shots at Navy Yard.— The Associated Press (@AP) July 2, 2015
UPDATE: Navy Yard officials now say a shooter has not been spotted and there are no casualties.
The Navy Yard in Washington D.C. has been locked down after shots were fired inside a building. Authorities are reporting there is an active shooter in the area. At this time there are no reports of casualties or injuries.
Earlier this week the FBI and Homeland Security issued a joint memo heightening security awareness and warning against lone wolf terror attacks over the July 4 weekend.
In 2013, the Navy Yard was attacked by a mentally ill man who killed twelve people.
More to come...
This post has been updated with additional information.