The driver of the vehicle was shot dead by police after lunging at officers with a knife.
An attack at the US Capitol complex in Washington DC has left one police officer dead and another in hospital with injuries.
A car crashed into a security barrier before the driver lunged towards the officers with a knife, police said.
The officers opened fire and the suspect was shot dead.
The city’s acting police chief has said the attack does not appear to be terrorism-related. An investigation has been opened.
“Whether the attack was at law enforcement, or whoever, we have a responsibility to get to the bottom of it and we’ll do that,” Robert Contee, the acting chief of Washington DC’s Metropolitan Police Department, said at a news conference on Friday.
“It is with a very, very heavy heart that I announce one of our officers has succumbed to his injuries,” Acting Capitol Police Chief Yogananda Pittman said at the conference.
In a later statement, Ms Pittman named the officer as William “Billy” Evans, who had been a member of the Capitol Police for 18 years.
“Please keep Officer Evans and his family in your thoughts and prayers,” she said.
The exact circumstances of the officer’s death are not yet clear.
Two law enforcement sources involved in the investigation told BBC partner CBS News that the suspect in the attack was 25-year-old Noah Greene from Indiana.
They added that no prior information about him had been found on any police databases, and that he did not appear to have any ties to the military.
There is an increased security presence around the Capitol building, where the US Congress sits, and a number of police cars surrounding the area.
The entry point on Constitution Avenue where the vehicle struck the barricade is frequently used by senators and staff.
But Congress is currently in recess, meaning the majority of politicians are not at the Capitol complex today.
President Joe Biden left Washington earlier in the day for Camp David, the presidential retreat in Maryland. The White House said the president has been briefed on the situation.
However, some reporters, maintenance workers and Capitol Hill employees are likely still on the Capitol grounds.
The lockdown order on the Capitol was lifted just after 15:00 local time. Officials said there was no ongoing threat.
Analysis by Samantha Granville, US Capitol
Capitol Hill has been tense over the past three months. Since the riot on 6 January, the complex has been like a fortress with barbed wire, metal fencing and heightened security.
But just weeks later, we are back here with blocked roads, extra troops, and a solemn feeling.
Congress is in recess today and staff I have spoken to are grateful to be home and nervous about returning to work after the Easter holiday.
They say, understandably, that it is scary to have your workplace attacked twice in a short space of time.
It is concerning for them that even with ramped up security, an event that led to an officer’s death still happened.
Shortly after 13:00 local time (18:00 GMT) the Capitol Police alert system sent an email to lawmakers and their staff ordering them to stay away from exterior windows and doors due to a threat. Anyone outside was instructed to seek cover.
At that time, a man driving a blue sedan had rammed the car into two officers standing at the North Barricade, according to police.
He exited the vehicle and ran towards the officers – at least one of whom drew a weapon and shot the suspect. The officers were then transported to hospital, one in an ambulance and one in a police cruiser.
Footage of the scene showed a helicopter flying overhead and what appeared to be two people on stretchers being moved into ambulances.
Onlookers were told to clear the area.
Police said the suspect died due to his injuries at 13:30 local time. Chief Contee told reporters the suspect appeared to act alone.
The FBI’s Washington Field Office is responding to the situation and is providing support to the Capitol Police. The US Attorney General is also aware of the incident and is being updated, according to CBS News.
The incident comes nearly three months after the deadly 6 January riot at the Capitol.