Former US President Donald Trump has pleaded not guilty in a Washington DC court to conspiring to overturn his 2020 election defeat.

During a short arraignment, he spoke softly to confirm his not-guilty plea, name and age, and that he was not under the influence of any substances.

He later told reporters the case was "persecution of a political opponent".

It marks the former president's third appearance in four months as a criminal defendant.

Mr Trump entered through a backdoor of the courthouse on Thursday afternoon in the centre of the nation's capital, just yards from the scene of the US Capitol riot that is central to the prosecution's case.

About 1,000 defendants charged with participating in the storming of Congress on 6 January 2021 have appeared in the same court building.

The former president seemed to exchange glances across the court with Jack Smith, the special counsel leading the investigation.

Mr Trump was seen twiddling his thumbs as he sat waiting for the hearing to begin, and he shook his head as the clerk read out the case number.

His not-guilty plea covered the four charges in this latest indictment:

The judge told the former president not to communicate about the facts of the case.

She warned him that failure to comply could result in an arrest warrant, revoked release conditions and contempt of court charges.

Prosecutors told the hearing the case would benefit from a speedy trial.

But Trump defence attorney John Lauro said they would need more time to prepare. He said the prosecution's timeline was "somewhat absurd" given that the investigation itself had taken three years.

The allegations laid out on Tuesday in an indictment, or charge sheet, include a count of "conspiracy to impair, obstruct, and defeat the federal government function through dishonesty, fraud and deceit".

Mr Trump lost the 2020 election to his Democratic challenger, Joe Biden, but he refused to concede and mounted weeks of challenges across several US states.

He is currently the frontrunner for the 2024 Republican White House nomination and may face a rematch with Mr Biden.

Speaking to reporters before flying home to New Jersey in his private plane, Mr Trump said his arraignment was a "very sad day for America".

He told reporters he was sad to see "the filth and the decay and all of the broken buildings and walls and the graffiti" in Washington DC.

Outside court, one of his lawyers previewed a possible defence strategy.

Alina Habba argued that the former president had been given bad guidance by his team in the aftermath of the election.

"I think that everybody was made aware that he lost the election, but that doesn't mean that that was the only advice he was given," said Ms Habba.

She added: "He may not agree with Mike Pence. He may not agree with one of his lawyers.

"But that doesn't mean there weren't other people advising him exactly the opposite. And the president has a right, as every one of us do, to listen to several opinions and make a decision."

The indictment lists six unnamed co-conspirators who allegedly helped Mr Trump plot to quash his election loss.

Three police officers who testified to Congress about their battle with Trump supporters during the US Capitol riot attended Thursday's court hearing. Several off-duty judges were also in the room.

A group of supporters waving Trump campaign flags assembled outside, along with anti-Trump demonstrators.

The next hearing will take place on 28 August and is expected to be procedural. However, the judge may set a trial date.

The Republican has already been charged in two other cases: with mishandling classified files and falsifying business records to cover up a hush-money payment to a porn star.

Mr Trump now faces five upcoming trials - three in New York, over the hush-money payment, and civil trials over business practices and alleged defamation of a woman who accused him of rape.

The fourth trial will take place in Florida relating to the alleged mishandling of classified documents.