A Capitol Police officer was killed and another injured after a man rammed his car into a security barrier outside the US Capitol and then got out of the vehicle and lunged towards the officers with a knife, setting off a major security scare nearly three months after the January 6 insurrection by pro-Trump supporters.

The 25-year-old suspect, identified as Noah Green, was shot dead by the Capitol Police.

"The incident happened around 1:02 PM on Friday (local time), when the suspect rammed his car into two of our officers and then hit the north barricade barrier. The suspect exited the vehicle with a knife in hand," Acting Capitol Police Chief Yogananda Pittman told reporters at a news conference.

At that time, the Capitol Police officers engaged that suspect, she said.

"He did not respond to verbal commands. The suspect did start lunging toward US Capitol Police officers, at which US Capitol Police officers fired upon the suspect. At this time, the suspect has been pronounced deceased," Pittman said.

Two US Capitol Police officers were transported to two different hospitals. One of them succumbed to his injuries, she said.

It was the second line-of-duty death in three months at the US Capitol Police department which bore the brunt of the unprecedented January 6 insurrection.

President Joe Biden said that he and the First Lady were heartbroken to learn of the violent attack at a security checkpoint on the US Capitol grounds, which killed William Evans of the US Capitol Police, and left a fellow officer fighting for his life.

We send our heartfelt condolences to officer Evans' family, and everyone grieving his loss. We know what a difficult time this has been for the Capitol, everyone who works there, and those who protect it, he said, adding that he has been receiving ongoing briefings from his Homeland Security Advisor, and will be getting further updates as the investigation proceeds.

Biden ordered that the flag of the United States shall be flown at half-staff at the White House and all federal buildings in honour of the deceased police officer.

"Today, in an inexplicable act of violence, a brave US Capitol police officer was killed in the line of duty, while another officer fights for his life. Officer William Evans made the ultimate sacrifice protecting the Capitol and those who work there on behalf of the American people. Officer Evans, his family, and all those who knew him are in our hearts and prayers. We mourn with them during this difficult time," Vice President Kamala Harris said.

"On this Good Friday, considered to be the saddest day of the year for some people of faith, our grief is deepened by the death of US Capitol police officer William Billy Evans," House Speaker Nancy Pelosi said in a dear colleague letter.

At a news conference, Washington DC Metropolitan Police Department Chief Robert Contee said that investigation was on and at this time it does not appear to be an ongoing threat.

"Obviously, we're in the very early stages of our investigation. We need to obviously understand the motivation behind this senseless act. It does not appear to be terrorism related," he said.

Pittman said that the suspect, Green, was not known to the police before Friday's attack. A review of Green's social media shows he posted in the weeks prior that he had lost his job and suffered medical ailments, and said he believed the federal government was targeting him with "mind control."

Less than two hours before he was shot and killed, Green posted a number of Instagram stories on an account that appears to belong to him, including links to other Instagram videos of Nation of Islam leader Minister Louis Farrakhan speaking, CNN reported.

"The U.S. Government is the #1 enemy of Black people!" a caption on one video read. In another post on the Instagram account, Green wrote last week that he believed Farrakhan had saved him "after the terrible afflictions I have suffered presumably by the CIA and FBI, government agencies of the United States of America."

The motivation of the suspect remained a mystery. On Facebook, Green had posted speeches and articles written by Farrakhan and Elijah Muhammad, who led the Nation of Islam from 1934 to 1975, that discussed the decline of the United States. Two law enforcement officials confirmed that the Facebook page, which was taken down Friday, had belonged to Green.

He had posted on Facebook about his personal struggles, especially during the pandemic.

“To be honest, these past few years have been tough, and these past few months have been tougher,” he wrote. “I have been tried with some of the biggest, unimaginable tests in my life. I am currently now unemployed, after I left my job, partly due to afflictions.”

He also spoke on Facebook about the “end times” and the Antichrist. On March 17, he posted a photograph of a donation he had made to the Norfolk, Virginia, chapter of the Nation of Islam, along with a video of a Farrakhan speech titled, “The Divine Destruction of America.”

Later that day, he encouraged his friends to join him in studying the teachings of Farrakhan and Muhammad.

The Nation of Islam is a Black nationalist movement that has advocated African American self-sufficiency. It has been condemned by the Southern Poverty Law Center for “the deeply racist, anti-Semitic and anti-gay rhetoric of its leaders,” including Farrakhan.

Green was born in West Virginia, attended high school in Virginia, then enrolled in Glenville State College, where he played football before transferring to Christopher Newport University in Newport News, Virginia. He played defensive back on the Christopher Newport football team and graduated in 2019 with a degree in finance.