Robert De Niro couldn't help but take a jab at Donald Trump in Cannes on Sunday, saying his character in the new film embodied the same kind of "evil" as the ex-president.

The legendary actor, 79, stars alongside Leonardo DiCaprio in Martin Scorsese's epic "Killers of the Flower Moon", which premiered to rave reviews at the Cannes Film Festival on Saturday.

He plays a real-life dignitary from 1920s rural America, William Hale, who built trust with local Osage Indians and then orchestrated dozens of murders in order to steal their oil-rich land.

"I don't understand a lot about him -- why he betrays them," De Niro admitted to reporters in Cannes.

"But we became a lot more aware after the murder of George Floyd with systemic racism and that's what this is," he said, referring to the police killing that sparked the Black Lives Matter protests.

"It's the banality of evil, it's the thing we've got to watch out for. We all know who I'm going to talk about -- I won't say his name," De Niro continued.

But a few moments later, the long-time Trump-hater couldn't hold back.

"It's like with Trump -- I had to say it," he said to laughter from the reporters. "There are people who think he could do a good job. Imagine how insane that is."

DiCaprio has received particular praise for his performance as a weak-willed man torn between his love for his Osage Indian wife and the evil plot in which he becomes embroiled.

'Love, trust and betrayal'

Calling the three-and-a-half-hour film "a reckoning with our past", the star was gushing with praise for Scorsese, saying: "He's able to expose the humanity of even the most twisted characters you can imagine.

"Marty's perseverence and ferocity to tell the truth, no matter how ugly... is masterful."

Scorsese said the film, which is due for general release in October, was not "a whodunnit -- it's a who didn't do it".

Adapting a best-selling nonfiction book, he chose to focus less on the criminal investigation which helped forge the FBI, preferring to focus on the central, poisonous love affair between DiCaprio's character and his wife, played by Lily Gladstone.

"It was a template for that tragedy of love, trust and betrayal of the indigenous people," Scorsese said.

Asked about still taking such risks in his filmmaking at the age of 80, Scorsese drew laughs from the crowd by saying: "What else am I going to do?"

De Niro said the world had seen enough films where "the good guy goes south or to Indian country and saves the day. This is much more important."