The Federal Capitol and all surrounding buildings were placed under preventive closure following the report of an external threat.
A later report indicates that at least one person was shot in the vicinity of the legislative body, but his condition and who he is is unknown.
In a Twitter post, NBC News correspondent Leigh Ann Caldwell commented on the situation, saying that a helicopter had landed nearby and that emergency management units are on site.
This is news in development, come back for future updates.