President Joe Biden on Thursday accused his predecessor Donald Trump of posing a continuing threat to American democracy in a speech on the anniversary of the deadly US Capitol attack by Trump supporters who tried to overturn his 2020 election defeat.

Speaking at the white-domed building that was the scene of the January 6, 2021, riot, Biden warned that Trump’s false claims that the election was stolen from him through widespread voting fraud could unravel the rule of law and undermine future elections.

“We must be absolutely clear about what is true and what is a lie.

Here’s the truth: A former President of the United States of America has created and spread a web of lies about the 2020 election. He’s done so because he values power over principle,” Biden said.

“He can’t accept he lost,” Biden added.

Launching such a direct attack on Trump — though Biden never actually said his predecessor’s name during the speech — was a departure for the President, who has spent most of his first year in office focused on pursuing his own agenda rather than looking backward.

But Democrats, a handful of Republicans and many independent observers have warned that the damage done by Trump’s efforts to undermine faith in the election he lost to Biden lingers on.

“The former President and his supporters have decided the only way for them to win is to suppress your vote and subvert our elections,” Biden said.

According to Reuters/Ipsos polling, some 55 per cent of Republican voters believe Trump’s false claim, which was rejected by dozens of courts, state election departments and members of Trump's own administration.

Accusing Trump of seeking to perpetuate a “big lie”, Biden said there is a “battle for the soul of America” and a struggle at home and abroad between the forces of democracy and autocracy.

Trump in a statement issued after the speech said that Biden “used my name today to try to further divide America”.

Four people died in the hours-long chaos a year ago, which occurred after Trump urged supporters to march to the Capitol and “fight like hell”. One police officer died the day after battling rioters and four later died by suicide. Around 140 police officers were injured.

One of the officers at the scene, Sergeant Harry Dunn of the Capitol Police, said the attack took an emotional toll.

“You cannot get away from January 6 even if you’re trying to. It’s everywhere, especially if it’s your place of work,” Dunn said in a phone interview. “Accountability needs to be had, no matter who that comes at.”

Biden’s remarks began a day-long series of events that will also feature House of Representatives Speaker Nancy Pelosi and other legislative leaders, mostly from Biden's Democratic Party.

Many Senate Republicans planned to be out of state attending the funeral of former Republican Senator Johnny Isakson.