A US Police officer has been killed after a man rammed a car into two officers at a barricade outside the US Capitol and then emerged wielding a knife, law enforcement officials said.
Video showed the driver of the crashed car with a knife in his hand and starting to run at the pair of officers, Capitol Police Acting Chief Yogananda Pittman told reporters.
The driver stabbed one of the officers, Ms Pittman said.
Authorities shot the suspect, later named as 25-year-old Noah Green from Indiana, who died at a hospital.
Both police officers were hospitalised, and one of them "succumbed to his injuries", Ms Pittman said.
The dead officer has been identified as William "Billy" Evans, an 18-year veteran of the force.
US President Joe Biden said he and his wife were heartbroken to learn of the attack and expressed condolences to Mr Evans's family.
He directed flags at the White House to be lowered to half-staff.
Investigators were digging into Green's background and examining whether he had any history of mental health problems as they tried to discern a motive.
The crash and shooting happened at a security checkpoint near the Capitol as Congress was on recess.
It comes as the Washington region remains on edge nearly three months after a mob of armed insurrectionists stormed the Capitol as Congress was voting to certify Joe Biden's presidential win.
Five people died in the January 6 riot, including Capitol Police officer Brian Sicknick, who was among a badly outnumbered force trying to fight off insurrectionists who supported former president Donald Trump's bid to overturn the election.
Authorities installed a tall perimeter fence around the Capitol and for months restricted traffic along the roads closest to the building, but they have begun pulling back some of the emergency measures in recent weeks.
There was no immediate connection apparent between January riot and Friday's crash.
"This has been an extremely difficult time for US Capitol Police after the events of January 6 and now the events that have occurred here today," said Ms Pittman.
She told reporters the suspect did not appear to have been on police radar. But the incident underscores that the building and campus remain potential targets for violence.
It occurred about 91 metres from the entrance of the building on the Senate side of the Capitol.
The security checkpoint is typically used by senators and staff on weekdays, but senators are away for recess.
Fencing that prevented vehicular traffic near that area was recently removed.
One of the officers who was injured was taken by police car to the hospital; the other was being transported by emergency medical crews, the officials said.
The US Capitol complex was placed on lockdown after the shooting and staff were told they could not enter or exit buildings.
US spy agencies warned in mid-March of an ongoing threat that racially motivated violent extremists, such as white supremacists, will carry out mass-casualty attacks on civilians while militia groups target police and government personnel and buildings.
Video and images from the scene showed a dark coloured sedan crashed against a vehicle barrier and a police K-9 inspecting the vehicle.
Law enforcement and paramedics could be seen caring for at least one unidentified individual.
Dozens of National Guard troops, who have been stationed at the Capitol since the January attack, quickly deployed.
Heavily armed and in riot gear, they jogged in columns to stand in rows at the scene and around the complex.
ABC/wires
