Donald Trump pleaded not guilty on Thursday to federal charges that he orchestrated a plot to try to overturn his 2020 election loss in what US prosecutors call an unprecedented effort by the then-president to undermine the pillars of American democracy.

Special Counsel Jack Smith, who has overseen the investigation, looked on from the front row as Trump entered his plea before US Magistrate Judge Moxila Upadhyaya.

"Not guilty," Trump said, emphasising the first word.

The arraignment, lasting about half an hour, took place just half a mile (1 km) from the US Capitol, the building Trump's supporters stormed on January 6, 2021, to try to stop Congress from certifying his defeat.

The plea - the third for Trump in four months - kicks off months of pretrial legal wrangling that will unfold against the backdrop of the 2024 presidential campaign, in which Trump is the front-runner for the Republican nomination to take on Democratic President Joe Biden.

In a 45-page indictment on Tuesday, Smith accused Trump and his allies of promoting false claims the election was rigged, pressuring state and federal officials to alter the results and assembling fake slates of electors to try to wrest electoral votes from Biden.

Trump, 77, faces four counts, including conspiracy to defraud the US, to deprive citizens of their right to have their votes counted and to obstruct an official proceeding. The most serious charge carries a maximum prison sentence of 20 years.

When the court deputy read aloud the name of the case - "United States of America v. Donald J. Trump" - the former president shook his head in disapproval.

The next court date in the case will be August 28 before US District Judge Tanya Chutkan, though Upadhyaya said Trump would not be required to attend. August 28 is five days after the first scheduled Republican primary debate. Trump has yet to say whether he will take part.

Chutkan intends to set a trial date at that time, Upadhyaya said. Trump's lawyer, John Lauro, registered an early objection, arguing that the magnitude of the case and the amount of materials involved could require a lot of time.

"What we desire utmost is the opportunity to fairly defend President Trump in this matter," he said.

Prosecutor Thomas Windom countered that the case should proceed as normal, including with a speedy trial.

Trump was released without travel restrictions. One of his conditions of release is that he not discuss the case with any witnesses unless accompanied by his lawyers.

Trump has portrayed the indictment, as well as the other criminal cases against him, as a "witch hunt" intended to derail his White House campaign. In a series of social media posts since Tuesday, he has accused the Biden administration of targeting him for political gain.

He previously pleaded not guilty to federal charges that he retained classified documents after leaving office and New York state charges that he falsified documents in connection with hush money payments to a porn star.

Trump may soon face more charges in Georgia, where a state prosecutor is investigating his attempts to overturn the election there. The Atlanta-area prosecutor, Fani Willis, has said she will file indictments by mid-August.

"I NEED ONE MORE INDICTMENT TO ENSURE MY ELECTION!" Trump wrote on his Truth Social media platform ahead of his Thursday court appearance.

TRUMP RETAINS POLLING LEAD

About half of Republicans said they would not vote for Trump if he were convicted of a felony, according to a new Reuters/Ipsos poll, underscoring the potential risks his legal entanglements pose for his candidacy. (Reuters)