Speaking after his court appearance, the former US president said: "When you look at what is happening this is a persecution of a political opponent. This was never supposed to happen in America.

"This is a persecution of a person that is leading by very, very substantial numbers in the Republican primary and leading Biden a lot. So if you can't beat him you persecute him or you prosecute him, we can't let this happen in America."

Barely an hour after facing a judge in Washington, Trump emailed his supporters to ask for cash - and claimed that he could face "561 years in prison for a crime I did not commit".

Insisting he was an innocent man, his email said: "You are why I could never give up our mission to save America - no matter how nasty and vicious the attacks ever got.

"I always knew this was the price I had to pay to run for president as a political outsider and restore power to YOU, the American people...

"But AMERICA is always worth it!"

Trump emotionless in court

On Thursday, Trump appeared emotionless as he pleaded not guilty to all four counts against him.

These include conspiracy to defraud the US; to deprive citizens of their right to have their votes counted; and to obstruct an official proceeding - interrupting Congress as it was certifying Joe Biden as president.

They relate to the January 6 riot on the US Capitol building, which prosecutors said was "an unprecedented assault on the seat of American democracy" that was "fuelled by lies" from the former US president.

Read more:
Who's running to be the next US president?
What are the investigations Donald Trump is facing?
Trump's defence strategy and how his legal team could challenge charges

The current charges - the most serious of which is the obstruction of an official proceeding and conspiracy to obstruct - are the third criminal case against the 77-year-old in the last six weeks.

In New York he was charged with falsifying business records in connection with an alleged hush money payment to porn actor Stormy Daniels, and faces 40 felony counts in Florida, accused of illegally retaining classified documents at his Mar-a-Lago estate and refusing government demands to return them.

Trump pleaded not guilty in both cases, which are set for trial next year.

The next hearing is due to take place on 28 August, five days after the first scheduled Republican primary debate. Trump is not obliged to attend.