Washington DC - Former President Donald Trump has sharpened his allegation that his Democratic successor has weaponized the US justice system against him, comparing Joe Biden's tactics to those of Hitler's Gestapo.

The Republican 2024 presidential candidate made the remark during a private meeting Saturday with top party leaders and wealthy donors at his Mar-a-Lago resort in Florida, according to a recording provided to US media by one donor.

In a 90-minute speech, Trump accused the Democrats of "running a Gestapo administration," referring to the secret police force in Nazi Germany.

"It’s the only way they’re going to win," he said.

Joe Biden Fade out: Biden disappears into background ahead of Trump inauguration

The "Gestapo" comment came as the campaign has begun heating up, and it follows several other Trump remarks that critics have said are dangerously inflammatory, including calling political rivals "vermin" and comparing immigrants to "animals."

His comments in Mar-a-Lago brought loud applause from the audience, which included a number of potential vice presidential picks, according to Politico.

He again lashed out at the prosecutors who have brought four separate court cases against him, including the hush money trial now taking place in New York.

Trump denounced what he claimed was a "witch hunt" hatched by the Democratic administration to eliminate his key presidential rival.

The Biden campaign, which has denied any role in the legal cases, responded Sunday, saying the Republican's angry remarks confirmed "what we already knew: Trump's campaign is about him. His fury, his revenge, his lies, and his retribution."