The U.S. Capitol and the buildings within its complex are on lockdown with police investigating.

Heavily armed U.S. Capitol Police officers stand guard a hallway at the basement of the Capitol. (Photo by Alex Wong/Getty Images)

There were no immediate details Tuesday. It marks the second time in less than a week that the Capitol has been locked down.

Police have sent an email to congressional staff advising them to close and lock doors and stay away from external doors and windows.

Both the House and Senate were in session, with House members voting. In the Senate, lawmakers were delivering speeches from the floor.

Tourists sat in the visitors' gallery in the Senate, apparently unaware of what was transpiring.

(Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.)


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