Sending the legislature building into an emergency lockdown, a car rammed a barricade outside the US Capitol on Friday afternoon, killing one police officer and leading to the driver being shot, USCP Acting Chief said.

One officer succumbed to the injuries and another officer was in serious condition. Meanwhile, the driver was has died after being shot, as per AFP inputs.

Yogananda Pittman said in a press briefing following the incident, "I just ask that the public continue to keep US Capitol Police and their families in your prayers", reported CNN. 

The crash and shooting happened at a checkpoint near the Capitol as Congress is on recess. 

The unnamed suspect wielded a knife while exiting the vehicle and did not respond to any of the verbal commands given by the officers present at the scene. 

Pittman added, "The suspect did start lunging toward US Capitol Police officers, at which time US Capitol Police officers fired upon the suspect. At this time the suspect has been pronounced deceased", reported CNN.

US Capitol Police said that all Capitol buildings are being locked down "due to an external security threat," the Associated Press reported. The staff members have been told that they cannot enter or exit the buildings. 

Initially, Capitol Police said someone "rammed a vehicle into two USCP officers" and the driver was taken into custody.

"A suspect is in custody. Both officers are injured. All three have been transported to the hospital," the US Capitol Police department said on Twitter.

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The US Capitol complex was placed on lockdown after the shooting and staff were told they could not enter or exit buildings.

The incident occurred about 100 yards (91 metres) from the entrance of the building on the Senate side of the Capitol, as per AP inputs. 

The security checkpoint is typically used by senators and staff on weekdays. Congress is currently on recess.

In recent weeks some security has been loosened, with the number of armed National Guard troops at the Capitol reduced and a security fence that created a broad perimeter around the Capitol complex removed.

The danger on Friday was limited as Congress was in recess and relatively few people were in the building.

But CBS News reported that security officials had already warned congressional staffers of a threat before the car-ramming.