A policeman has died after a driver rammed a car into two officers at a barricade outside the US Capitol and then emerged wielding a knife, officials say.

Both officers were hospitalised and one of them died from his injuries, Capitol Police Acting Chief Yogananda Pittman told reporters.

The suspect died in hospital after he was shot by police when he attempted to lunge at them with a knife outside the building in Washington DC on Friday.

Multiple media organisations, citing anonymous sources, named the suspect as Noah Green, 25, of Newport News, Virginia. Green’s brother told the Washington Post that his sibling struggled with drug use and paranoia and his family worried about his mental state.

According to media reports, Green spoke on Facebook about the “end times”, the anti-Christ, and government “mind control”. He also said he was unemployed after leaving his job, “partly due to afflictions,” and praised Nation of Islam leader Louis Farrakhan.

Mentally troubled

Facebook said in a statement that it removed the suspect’s accounts from Facebook and Instagram and were in contact with law enforcement.

“Clearly this was someone who was actively trying to just get at whoever or whatever – we just don’t know right now,” Contee said.

“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.”

The dramatic attacked sparked a lockdown of the US Capitol, which has since been lifted, as the National Guard was also called in.

White House secretary Jen Psaki said President Joe Biden was “aware” of the attack. Mr Biden had left for Camp David when the incident happened.

“The suspect entered what we refer to as the north barricade of the Capitol,” Police Acting Chief Pittman said.

“The suspect rammed his car into two of our officers and then hit the north barricade barrier.

“At such time the suspect exited the vehicle with a knife in hand. Our officers then engaged that suspect. He did not respond to verbal commands.”

Officer 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.”

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 incident and the January 6 riot.

-with AAP