WASHINGTON, United States (AP) — A Capitol police officer was killed Friday 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.

The suspect died at a hospital, officials said. Both officers were hospitalised, and one of them “succumbed to his injuries,” Capitol Police Acting Chief Yogananda Pittman told reporters.

Pittman did not identify the slain officer or suspect. Authorities said that there was no longer an ongoing threat and that the attack did not appear to be related to terrorism. There was also no immediate connection apparent between Friday's crash and the January 6 riot.

The crash and shooting happened at a security checkpoint near the Capitol as Congress is 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 6 and Friday's crash. Pittman said 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 100 yards (91 meters) 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 lawmakers are away for recess. Fencing that prevented vehicular traffic near that area was recently removed.

The officials initially said the suspect was being taken to the hospital in critical condition. 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. Video showed National Guard troops mobilising near the area of the crash.

Video posted online 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.

President Biden had just departed the White House for Camp David when the incident occurred. As customary, he was traveling with a member of the National Security Council Staff who was expected to brief him on the incident.