The area has been evacuated as security agencies carry out their work.
A large number of police officers, and other law enforcement personnel, are on the scene.
US Capital Police said they are “responding to a suspicious vehicle near the Library of Congress”.
The Library of Congress is situated near both the Capitol building and US Supreme Court.
Speaking on condition of anonymity, law enforcement officers said they are trying to establish whether it is a viable explosive device.
On January 5 pipe bombs were left outside the headquarters of both the Democratic National Committee, and the Republican National Committee, in the capital.
Neither exploded and there were no reports of any injuries.
The following day Congress was stormed by thousands of pro-Trump rioters, angry at the November 2020 presidential election result.
More to follow…