U.S. Capitol Police say they are conducting an active bomb threat investigation near the Library of Congress, across from the U.S. Capitol.

In a tweet, the police says the threat is related to a suspicious vehicle. Several streets in the area have been closed. The FBI says its Washington field office is responding along with agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives.

The Library of Congress has evacuated the historic Jefferson Building. Washington's transit agency says subway trains are bypassing the nearby Capitol South station.

Neither the House nor the Senate is in session, and most lawmakers are not in their offices.

This is a developing story.

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