The U.S. Capitol Police Department says one of its officers has died and another is injured after being rammed by a vehicle outside the building Friday afternoon.
Authorities flooded the surrounding streets on high alert after the attack in Washington.
William Evans, 18, has been named as the US Capitol police officer killed by the auto ramming. The officer's identity was not released. "So I ask that you keep our U.S. Capitol Police family in your thoughts and prayers". The driver of the auto was shot by police and taken to a hospital in critical condition.
Police said they did not yet know what had motivated the attacker, and they did not identify him.
But the attack underscores that the building and campus - and the officers charged with protecting them - remain potential targets for violence.
The crash and shooting happened at a security checkpoint near the Capitol as Congress was on recess.
The suspect drove a vehicle into the officers, got out of the auto and lunged at them, with a knife in his hand, Yogananda Pittman, acting chief of the United States Capitol Police, told a news conference.
Acting Chief of Capitol Police Yogananda Pittman speaks during a press conference near the US Capitol on April 2, 2021, after a vehicle drove into US Capitol police officers in Washington, DC. Law enforcement sources tell ABC News the suspect is dead.
The other injured officer is being treated an area hospital.
The officials could not discuss the matter publicly and spoke to the AP on condition of anonymity.
The U.S. Capitol was placed under lockdown amid what Capitol Police described as "an external security threat".
It also reported that incident occurred on the Senate side of the Capitol building.
Temporary fencing that had been erected around the Capitol's outer perimeter was removed late last month, though temporary fencing remains in place closer to the building.
The entry point on Constitution Avenue where the vehicle struck the barricade is directly where Senators and their staff come to the Capitol each day, according to observers.
Video and images from the scene showed a dark coloured sedan crashed against a vehicle barrier and a police K-9 inspecting the vehicle.